Ok, having identified the true source of the problem, a little searching has turned up the solution.
This thread here had the solution: Crystal Reports Crash App when Setting SetDataSource(DataSet)
I had set up the app.config file long ago to make Crystal Reports 13 work with my VB,NET app on my computer, but what I didn't know was the app.config needed to be included separately along with the .EXE file to the client PCs. Something I've never needed before when it was a .NET 2.0 application.
James
