I had this problem when trying to delete files from a temp folder I created in-code. I couldn't delete the temp folder because - for some reason - blitz refused to delete some files contained in it. Hmm, or was it the folder itself I couldn't delete?! Can't really remember.
Anyway, the only way I could get it to work was to do a EndGraphics before trying to delete the files! :/
Go figure.
[edit] Just checked. It was defo DeleteFile, not DeleteDir I was having the problem with. Using EndGraphics to 'fix' the prob was OK in my case because I was only deleting the temp folder when closing down the app, anyway. May not be a viable solution for you, though.
Anyway, the only way I could get it to work was to do a EndGraphics before trying to delete the files! :/
Go figure.
[edit] Just checked. It was defo DeleteFile, not DeleteDir I was having the problem with. Using EndGraphics to 'fix' the prob was OK in my case because I was only deleting the temp folder when closing down the app, anyway. May not be a viable solution for you, though.