I'm implementing a Visitor Group Criterion which allows the user to select a category. I've borrowed the code from the built-in Visited Category Criterion but when I save the Visior Group I get an error saying "Failed to convert item". I'm debugging my solution when I do this and there's no sign of an exception being throwin in the Output window for me to latch onto. I'm at a loss.
I've found this blog post but it lacks any real explanation for the issue:
What's causing the "Failed to convert item" error?
I'm using latest EPiServer.
Can you provide the code for your visitor group criterion and model?