SVN commit failed error

After running through a lot of merges last night (I was incrementally going through several changesets to see where I'd introduced an interesting regression) and updating to the HEAD revision and fixing the bug, I got the following error message while trying to commit:

svn: Commit failed (details follow):
svn: Your file or directory '' is probably out-of-date
svn: The version resource does not correspond to the resource within the transaction.  Either the requested version resource is out of date (needs to be updated), or the requested version resource is newer than the transaction root (restart the commit).

A svn up didn't fix the issue and neither did running svn clean.

The file in question is in a folder called /lib so in the end, I fixed it by deleting that folder (rm -rf lib) and then running svn up to restore the folder from the HEAD revision.

The only other advice I found about this on the net suggests that you delete the all-wcprops file in your .svn folder but I personally think that that's a Bad Idea (tm) as you don't want to go messing inside your .svn folders and corrupt your working copy.