just try setgenerate true -1. or specify core
working ok on windows
same error

Are you on Windows 8?
I was having the same problem, until I tried on a Win 7 VM, and it's working.
But..... the wallet is mining on a single thread.. have you guys noticed the same? (yes, I set more than 1 thread)
I'm on Windows 7. For both launches mine mined fine (say that 3 times fast) at first, but then I started getting the error consistently.