Is this a problem?
Windows 7 64-bit, Catalyst 13.8b2, 1 x 6950, 2 x 6970, oclhashcat 0.15RC4

First time I see that message. What can be the causes?

Quote:Flushing the password buffer failed

It happened at the last attack of a .bat file. The attack consisted of -a 0 on -m 300 on a wordlist directory + 2 sets of rules.
Please do not use Catalyst 13.8b2, see here:

It's known for silently discarding valid cracks!

I've added a special 13.8beta2 check into the host tools to inform the user about the problem.

Still, that does not explain the Flushing the password buffer failed error, have to look into it.