No, it is memory, no doubt about it. Which components did you increase memory for?
I assume this is upload via the browser, not import in the Configuration Tool?
If so, then any of the 3 components (Aware IM Server, Tomcat and JBoss) may need the memory increased - you need to play with all 3. If you just increased the memory for the Aware IM Server, for example, it might not have solved the problem, because some other component is running out of memory. My guess is that it's JBoss in this case.