Java Out of Memory Errors

Server 2008 R2

Java 7.U21

Openfire 3.81 + Fastpath.

I can only get about 5-7 days of uptime and then I start getting Java out of memory errors. This is a VM with 8 cores and 8GB of ram dedicated to it but I have never been able set Openfire to use more then 1024.

Running Openfire as a service, I have setup the openfire-server.vmoptions file with this in it.

-Xms256m

-Xmx1024m

If I increase it higher then 1024 the service will not start.

I have about 500 users on the server and more planned if I can keep it stable.