Although it was another problem that brought me to your thread, the solution to many Magento errors is kinda similar.
I also got one of those “There has been an error processing your request” and none of the usal actions worked:
1) deleting every cache file -> No effect.
2) creating custom temp folders -> No effect
3) asking my provider to increase database capabilities -> No effect.
What solved it was brute force, and i am not happy with this:
I disabled the whole error processing by opening ‘errors/report.php’
and commenting out // $processor->processReport();
To make sure it was the reason I reenabled it and it STILL worked… So actually I changed nothing.
Seems to force kind of a restart…