If you try to do a Clean and Build on a project that is a web service deployed 
on a web container, such as Glassfish, you get a message about a file that 
can't be deleted.

There is no indication why. On a hunch, I stoped Glassfish and then did the
Clean and Build. This time there was no problem. 

The Clean and Build function should either automatically recycle the web server 
or at least display a possible reason that the file can't be deleted, such as it
being in use by the web server associated with the web service.

Note that on Deploying the service, NB automatically starts glassfish, so this
request is not too far fetched.