If you suspend a task on your first GPU (for example to run a beta) and allow another task to complete on a different GPU, you will not download any new tasks (as you have suspended one task).
Should you then resume the suspended task, it will try to run on the available GPU!
As it was initially running on the first GPU it will error when it tries to start on a different GPU.

This occurs when you have Boinc configured to suspend tasks and keep them in memory.
This might not happen if suspended tasks are saved to disk.

So, don’t suspend one task at a time!
If you have to, suspend the project or just use Snooze GPU.

Thanks for the heads-up.

My guess on your question of whether the WU would fail if you saved to disk is that everything will be OK. I switched physical cards out from underneath 3 WUs on two different machines and they all completed fine.

<OT>
I switched an eVGA 295 for a BFG 285 OC and vice versa to test runtime differences between Vista64 and XP32. XP32 seems to be a little faster (5%) but that may be a side effect of turning HT off on my i7.
</OT>

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Thanks - Steve