I'm having similar issues. I went from 4.9.0 to 4.9.5 with no issue.

Trying from 4.9.5 to 5.1.4 (on a copy of my site) My error is on the following two lines:

Executing Application Upgrades: 05.00.00 Error!
Installing Package File HTML_Community_05.01.04_Install:  Error!

After the upgrade process runs none of my Text/HTML modules have content and I can't log into the site.
The log file for 05.00.00 is blank

I tried re-running the SQL upgrade scripts for 05.00.00 and HTML_Community_05.01.04

The sql for the Community runs ok, just a few errors on dropping columns (since they were already dropped during the upgrade process.
The sql for Application Upgrades took 20 minutes to run (!) and again, the only erros I see are attributable to it having run 2x (once during the upgrade and them me running it again.

I'm seeing a fair number of people having similar issues, but haven't seen a solution that seems reasonable yet.

I'm going to look at the EventLog next, but since I can't log into the site, I need to parse the XML into a readable format first.

I tried reinstalling the HTML module through Extensions and it failed again.  This is the output:

See below for the results of the package installation

Error loading files from temporary folder - see below StartJob Starting Installation Info Starting Installation - DNN_HTML Info Starting Installation - Script Info Begin Sql execution Info Creating backup of previous version - Providers\DataProviders\SqlDataProvider\05.01.00.SqlDataProvider Info Created - Providers\DataProviders\SqlDataProvider\05.01.00.SqlDataProvider Info Executing 05.01.00.SqlDataProvider Info Start Sql execution: 05.01.00.SqlDataProvider file Failure SQL Execution resulted in following Exceptions: System.Data.SqlClient.SqlException: Column names in each table must be unique. Column name 'ItemID' in table 'dbo.HtmlText' is specified more than once. at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection) at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection) at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj) at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj) at System.Data.SqlClient.SqlCommand.RunExecuteNonQueryTds(String methodName, Boolean async) at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult result, String methodName, Boolean sendToPipe) at System.Data.SqlClient.SqlCommand.ExecuteNonQuery() at DotNetNuke.Data.SqlDataProvider.ExecuteADOScript(String SQL) at DotNetNuke.Data.SqlDataProvider.ExecuteScript(String Script, Boolean UseTransactions) IF NOT EXISTS (select * from dbo.sysobjects where id = object_id(N'dbo.HtmlTextLog') and OBJECTPROPERTY(id, N'IsTable') = 1) BEGIN ALTER TABLE dbo.HtmlText ADD ItemID int NOT NULL IDENTITY (1, 1), Content ntext NULL, Version int NULL, StateID int NULL, IsPublished bit NULL, CreatedByUserID int NULL, CreatedOnDate datetime NULL, LastModifiedByUserID int NULL, LastModifiedOnDate datetime NULL ALTER TABLE dbo.HtmlText ADD CONSTRAINT PK_HtmlText PRIMARY KEY CLUSTERED ( ItemID ) ON [PRIMARY] END System.Data.SqlClient.SqlException: The transaction log for database 'NCGTDNN' is full. To find out why space in the log cannot be reused, see the log_reuse_wait_desc column in sys.databases at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection) at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection) at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj) at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj) at System.Data.SqlClient.SqlCommand.RunExecuteNonQueryTds(String methodName, Boolean async) at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult result, String methodName, Boolean sendToPipe) at System.Data.SqlClient.SqlCommand.ExecuteNonQuery() at DotNetNuke.Data.SqlDataProvider.ExecuteADOScript(String SQL) at DotNetNuke.Data.SqlDataProvider.ExecuteScript(String Script, Boolean UseTransactions) IF NOT EXISTS (select * from dbo.sysobjects where id = object_id(N'dbo.HtmlTextLog') and OBJECTPROPERTY(id, N'IsTable') = 1) BEGIN update dbo.HtmlText set Content = DesktopHtml, Version = 1, IsPublished = 1, CreatedByUserID = CreatedByUser, CreatedOnDate = CreatedDate, LastModifiedByUserID = CreatedByUser, LastModifiedOnDate = CreatedDate ALTER TABLE dbo.HtmlText DROP COLUMN DesktopHtml, DesktopSummary, CreatedByUser, CreatedDate CREATE TABLE dbo.HtmlTextLog ( HtmlTextLogID int NOT NULL IDENTITY (1, 1), ItemID int NOT NULL, StateID int NOT NULL, Comment nvarchar(4000), Approved bit NOT NULL, CreatedByUserID int NOT NULL, CreatedOnDate datetime NOT NULL ) ON [PRIMARY] ALTER TABLE dbo.HtmlTextLog ADD CONSTRAINT PK_HtmlTextLog PRIMARY KEY CLUSTERED ( HtmlTextLogID ) ON [PRIMARY] CREATE TABLE dbo.HtmlTextUsers ( HtmlTextUserID int NOT NULL IDENTITY (1, 1), ItemID int NOT NULL, StateID int NOT NULL, ModuleID int NOT NULL, TabID int NOT NULL, UserID int NOT NULL, CreatedOnDate datetime NOT NULL ) ON [PRIMARY] ALTER TABLE dbo.HtmlTextUsers ADD CONSTRAINT PK_HtmlTextUsers PRIMARY KEY CLUSTERED ( HtmlTextUserID ) ON [PRIMARY] ALTER TABLE dbo.HtmlText WITH NOCHECK ADD CONSTRAINT FK_HtmlText_WorkflowStates FOREIGN KEY ( StateID ) REFERENCES dbo.WorkflowStates ( StateID ) ON UPDATE NO ACTION ON DELETE NO ACTION NOT FOR REPLICATION ALTER TABLE dbo.HtmlTextLog WITH NOCHECK ADD CONSTRAINT FK_HtmlTextLog_HtmlText FOREIGN KEY ( ItemID ) REFERENCES dbo.HtmlText ( ItemID ) ON UPDATE NO ACTION ON DELETE CASCADE NOT FOR REPLICATION ALTER TABLE dbo.HtmlTextLog WITH NOCHECK ADD CONSTRAINT FK_HtmlTextLog_WorkflowStates FOREIGN KEY ( StateID ) REFERENCES dbo.WorkflowStates ( StateID ) ON UPDATE NO ACTION ON DELETE NO ACTION NOT FOR REPLICATION ALTER TABLE dbo.HtmlTextUsers WITH NOCHECK ADD CONSTRAINT FK_HtmlTextUsers_HtmlText FOREIGN KEY ( ItemID ) REFERENCES dbo.HtmlText ( ItemID ) ON UPDATE NO ACTION ON DELETE CASCADE NOT FOR REPLICATION END Info End Sql execution: 05.01.00.SqlDataProvider file Info Finished Sql execution Failure Installation Failed - Script Info Installation Failed - DNN_HTML Info Deleted temporary install folder EndJob Installation Failed

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Cheers
Dave

I received the following error when trying to upgrade from DNN 5.6.2 -> 5.6.8
...
00:00:00.703 - Updating Config Files: 05.06.08 Success
00:00:00.703 - Performing General Upgrades
00:00:00.968 - Installing Optional Modules:
00:00:00.984 - Installing Package File HTML_Community_05.01.04_Install: Error!
00:00:01.796 - Installing Package File HTML_Community_05.02.00_Install: Error!
00:00:02.203 - Installing Package File HTML_Community_05.04.03_Install: Error!
00:00:02.656 - Installing Package File HTML_Community_05.06.00_Install: Error!
00:00:03.296 - Installing Package File HTML_Community_05.06.02_Install: Error!
00:00:03.640 - Installing Package File HTML_Community_05.06.08_Install: Error!
00:00:04.078 - Installing Package File Messaging_05.06.05_Install: Success
...

I then tried to re-install the module package via the Host > Extensions manager and received the following error:
See below for the results of the package installation
Error loading files from temporary folder - see below
StartJob Starting Installation
Info Starting Installation - DNN_HTML
Failure Package Installation aborted - DNN_HTML
Failure Package Installation aborted
Info Installation Failed - DNN_HTML
Info Deleted temporary install folder
EndJob Installation Failed

Any help would be appreciated.