RAD - Portal - can't delete log4j.properties

Sometimes when I am working in RAD (6 or 7) on a Portal (5.1) project, it fails to re-build, saying that it cannot delete ./web/WEB-INF/classes/log4j.properties.

Often I can solve this with rm -f ./web/WEB-INF/classes/log4j.properties, but not always. Other times I need to re-build the app and delete the command quickly while that starts!

Worst case: I have had to close the server. Once I had to close RAD itself.