CR XI.5 Rev 2 cant Connect to 2005

I'm trying to move my datasource from SQL 2000 to 2005 for CR XI.5 Rev 2, but when I switch to 2005, CR throws an error

"database logon failed"... I know, I know it's a general error, but maybe where it fails in the code may be a clue?

report.Export(exportOptions);

where ExportFormatType is PDF

Any advice would be much appreciated!!