PermGen space error

I have a soapui test that contains more than 20 project; each project contain different groovy test case

If execute all the project, after the execution of same projects I have the following error: An error occurred [PermGen space].

I modify the soapui.bat file adding the "-XX:MaxPermSize=512m" parameter to JAVA_OPTS but the problem is still present.

Any suggestion on how fix the problem ?

Regards

Massimo