I have upgraded from 3.3.4 to 4.3.4 - now I have some problems.
One of them is the log viewer not available.

Error: Log Viewer is currently unavailable.
DotNetNuke.Services.Exceptions.ModuleLoadException: Cannot resolve collation conflict for equal to operation. ---> System.Data.SqlClient.SqlException: Cannot resolve collation conflict for equal to operation. 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.SqlDataReader.ConsumeMetaData() at System.Data.SqlClient.SqlDataReader.get_MetaData() at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString) at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async) at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result) at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method) at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method) at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior) at Microsoft.ApplicationBlocks.Data.SqlHelper.ExecuteReader(SqlConnection connection, SqlTransaction transaction, CommandType commandType, String commandText, SqlParameter[] commandParameters, SqlConnectionOwnership connectionOwnership) at Microsoft.ApplicationBlocks.Data.SqlHelper.ExecuteReader(String connectionString, CommandType commandType, String commandText, SqlParameter[] commandParameters) at Microsoft.ApplicationBlocks.Data.SqlHelper.ExecuteReader(String connectionString, String spName, Object[] parameterValues) at DotNetNuke.Services.Log.EventLog.DBLoggingProvider.Data.SqlDataProvider.GetLog(Int32 PageSize, Int32 PageIndex) at DotNetNuke.Services.Log.EventLog.DBLoggingProvider.DBLoggingProvider.GetLog(Int32 PageSize, Int32 PageIndex, Int32& TotalRecords) at DotNetNuke.Services.Log.EventLog.LogController.GetLog(Int32 PageSize, Int32 PageIndex, Int32& TotalRecords) at DotNetNuke.Modules.Admin.Log.LogViewer.BindData() at DotNetNuke.Modules.Admin.Log.LogViewer.Page_Load(Object sender, EventArgs e) --- End of inner exception stack trace ---

What can I do to fix this ?

The problem is most likely the same thing I had happen.  Something weird going on with the database collation settings.  The log viewer calls a stored procedure that uses a temporary table, and this temporary table somehow ends up with a different collation.

Altering the stored procedure GetEventLog and set a collation value for the LogGUID column in the #PageIndex temporary table fixed the issue for my sites.

i.e.

LogGUID varchar(36) collate database_default

Hi

Collation name for this db is: SQL_Latin1_General_CP1_CI_AS
Don't ask me, what it stands for