Bad version number in .class file

I need a new free java server because myjavaserver.com, free host that i use for along time has a problem. My friend tell me to check out eatj.com, another free java host. I think it's great for doing a test. I just register for a free account and upload my testing web app to it. Testing my first apps give me "Bad version number" as you see below.

javax.servlet.ServletException: Bad version number in .class file

I guess these caused by eatj.com tomcat is running with j2se 1.5 but I compile my servlet with j2se 1.6.
Anyway, the problem is easily solve by recompile with option -target 1.5.