Well, here's some basic questions:
Which Catalyst driver do you have?
What OpenCL version do you have?
Have you installed the ATI Stream SDK?
I know these seem silly, since you're able to complete CC tasks; they are still relevant, however.
I used to receive strange errors a long time ago (usually at the start of a task) and it turned out to just be the result of a specific Catalyst driver. Coincidentally, I was even able to run Collatz tasks just fine, as well.