No problem; thanks for clarifying that. And, I was actually thinking the same thing about BeginReadMultiSample. Please do try using that instead and let me know how it goes.
I changed the calls from BeginMemoryOptimizedReadMultiSample and EndMemoryOptimizedReadMultiSample to BeginReadMultiSample and EndReadMultiSample, and got no exceptions.
I still want to understand what was the problem though,
Glad to hear that it's working! I'm not sure why the non-optimized version of the function's working. There aren't any differences in the documentation that jump out at me. I can consult with a colleague, but this may just be a one-off case of strange behavior exclusive to your machine.
