"Attempted to read or write protected memory. This is often an indication that other memory is corrupt."
After several rounds of machine reboots, file checking, and messing with the connection manager, I finally checked the actual query being executed (I know, way to work backwards). It had a parameter being passed in that must have been hand-entered, because it was lacking the namespace, i.e.
Corrected that, and everything worked fine. So the error message is thoroughly misleading, but if you investigate the query execution, you may find a bad parameter name.