For some weeks null-reference exceptions have been logged in events by the scheduler. It was the search indexer that was causing the exception. I decided to clean the search-index tables and rebuild the index from scratch. When I try to rebuild the index I get the following exception:

Error: Search Admin is currently unavailable.
DotNetNuke.Services.Exceptions.ModuleLoadException: Value cannot be null. Parameter name: format ---> System.ArgumentNullException: Value cannot be null. Parameter name: format at System.String.format(IformatProvider provider, String format, Object[] args) at System.String.format(String format, Object[] args) at DotNetNuke.Modules.Reports.Exceptions.ReportsModuleException.get_Message() at System.Exception.ToString() at DotNetNuke.Services.Log.EventLog.ExceptionLogController.AddLog(Exception objException, ExceptionLogType LogType) at DotNetNuke.Services.Exceptions.Exceptions.LogException(Exception exc) at DotNetNuke.Services.Search.ModuleIndexer.GetSearchIndexItems(Int32 PortalID) at DotNetNuke.Services.Search.SearchEngine.GetContent(IndexingProvider Indexer) at DotNetNuke.Services.Search.SearchEngine.IndexContent() at DotNetNuke.Modules.Admin.Search.SearchAdmin.cmdReIndex_Click(Object sender, EventArgs e) --- End of inner exception stack trace ---

Thanks to Fuji Nguyen excellent write up on how to compile and debug the Reports module source.

I have managed to track down the problem. Actually, it's two problems. One problem regarding the use of parameters in the reports module and another problem with exception logging.

When the search indexer calls the ReportsController.GetSearchItems()  the parameter collection that is passed down to the DotNetNukeDataSource instance will be empty. If the query requires one or more parameters (@TabId in my case) the SQL will fail because of the missing parameter. An exception will be thrown from line 50 in DotNetNukeDataSource.vb.

When the exception is being logged the Message property in ReportsModuleException.vb will fail yet again and obscure the original exception message:

        Public Overrides ReadOnly Property Message() As String
            Get
                Dim localized As String = String.Empty
                If Not String.IsNullOrEmpty(_resourceFile) Then
                    localized = Localization.GetString(_resourceKey, _resourceFile)
                Else
                    localized = Localization.GetString(_resourceKey)
                End If
                If _formatArgs IsNot Nothing AndAlso _formatArgs.Length > 0 Then
                             Return String.format(localized, _formatArgs) <-- localized Is Nothing!!
                Else
                    Return localized
                End If
            End Get
        End Property

Instance field values:
_resourceKey = "SqlError.Text"
_resourceFile = "/DataSources/DotNetNuke/App_LocalResources/DataSource.ascx.resx"
_formatArgs = {Length=2}
               {0} = "1"
               (1) = "Must declare the scalar variable "@TabId"."

The error reporting can't resolve the value for "SqlError.Text". Could it be the resource file name that is incorrect?

Can the missing parameters be added for the GetSearchItems() method also? I know @UserId must be set to Null, but the other parameters like @TabId, @PortalId and @ModuleId are known when the indexer is running.

Found the solution to my installation problem. Looks like it's not possible to get the source code file to install properly into the App_Code folder. But if I create a compiled assembly using the steps provided by the Packaging your DotNetNuke module tutorial the resulting assembly for my source code file can be added to the installation package. The data source extension will now install correctly. I will put it up for download within the next few days.