Illustra VACUUM problem

Hi, I've been using Illustra for a couple of months without any problems... until now, that is. We have a script that automatically updates our database by parsing and import external data. The script ends with a database dump followed by a vacuum, which was working fine. However, the vacuum has recently stopped working, barfing up the following error; XLV001:vacuum: cannot create lock file -- another vacuum command running? There most certianly isn't another vacuum running, so can anyone help me clear this block? Is there a lock I can undo somewhere? Thanks in advance. Love & Life, G.