We spent most of an afternoon trying to figure out a problem we were having with Android in-app purchases. We'd try to buy something, it would fail, and in the log output we'd get IAB_PERMISSION_ERROR, something that you'll find almost no hits on if you do a Google search.
After a lot of pounding our heads on the wall, we figured out the source of the problem, at least in our case -- the item we were trying to buy existed but hadn't yet been published. Sounds obvious I know, but it wasn't our Market account we were testing against so we didn't have any way to double-check it ourselves, and were told everything was good to go.
If you got here because you had this error happen and this is the only link in English, I suggest that you confirm the in-app product has actually been published, not just saved. We also did some tests trying to access an in-app product from an account that wasn't in the test list, you'll see the same error in that case.