Frequently when working in a Java EE7 project I will get an error like.

"The project was not built due to "Could not delete '/gp-server/target/classes/META-INF`.". Fix the problem, then try refreshing this project and building since it may be inconsistent.

I've looked into a process explorer in windows and then this case is happening there is always a javaw.exe process with a file handle to "V:\workspace\gp-server\target\classes\META-INF\persistence.xml

It looks like either jboss tools or eclipse is holding on to a file handle for this.