It sounds like something else might be accessing the directory at the time you’re trying to delete it. The usual suspects are antivirus tools, and indexing tools like Google Desktop.
As a “quick n dirty” fix, each action has a “retry count” you can set with a pause value between tries. This can be accessed on the Runtime tab for the action. Set the retry count to 4 or 5 and FinalBuilder will try multiple times before failing out.
I bet you're right. I've got Windows Desktop Search running, and I'm sure it's got that pesky indexing service running, "helping me" by indexing all my temporary source files.
I hit this problem all the time. It’s a major pain in the arse, but it doesn’t seem to be FinalBuilder’s fault. The “retry” method mentioned usually works…
In many cases, what you actually really want is to clean out the directory rather than to delete it, so also see if you can replace the “delete directory” with “delete files”, which stands a better chance of working.