Sometimes there are GC problems without any OOMEx, you might enable gc logging. Also the GC might have issues and produce such failures.
You might change the GC.
Also You might give Java6 a try with the latest version
The your webapp uses a lot theard?
I think you should do an Tunig on JVM
Why you use this parameter?
Memory: -Xms1024m -Xmx7120m -XX:MaxPermSize=1024m