"Delete Folder" doesn't work sometimes

[ambalboa]

This is weird but sometimes the 'Delete Folder' action step doesn't work, giving me the following error message:

7/9/2007 2:39:50 PM: Building project step 'Delete Folder'...
7/9/2007 2:39:50 PM: Building project step 'Delete Source Code folder'...
Deleting folder 'C:\Release\1.2.3 Release\Source Code'...
The directory is not empty.

Process completed with exit code 145
7/9/2007 2:39:50 PM: Step 'Delete Source Code folder' failed

Now, the option "Delete subfolders" is checked, so even if the folder specified in the path wasn't empty, it should still delete it and everything in it, right? This happens every now and then. I ran the step a second time and it worked. Why did this happen?