I have a Tomcat v7.0 server setup in my eclipse (helios) environment which I use for testing web applications. Currently I have in my workspace a struts web-app which is loaded
I have encountered the same problem. You are not required to do something extra ordinary. Two solution might be helpful.
1) Restart your IDE (i.e. eclipse). (This might help you because in my case it did)
2) Restart your computer. This will help you to unlock the lock beyond any doubt.
Note: Cleaning Tomcat Work Directory may not help in your case.