I have a set of Crystal Reports that has been working for a long time. Recently, a small subset of updated reports are now prompting one of my users for database connection information when the report starts:

There is a default connection in the report but only the server gets picked up, not the catalog.
This behaviour only happens on the one machine, none of my other users are experiencing problems. The function that sets the database connection was copied from one of Don's examples, long ago. We have recently upgraded all users to V22, but only one user is experiencing this strange problem and only with 2 reports - unfortunately the ones they use most often.
I have a standard report form with the Crystal Report Viewer embedded in it. This form uses the same code for all reports: 1 - set parameters, 2 - set database connection for report and all sub-reports.
Does anyone have any suggestions on how to debug this? I have been unable to see any differences between the users connection information (in a domain) on that machine vs any other machines. Needless to say, it works fine in development and is not reproduceable.
The environment is Visual Studio 2010, Visual Basic, SQL Server 2005.
Thanks, Neil