logic2sonar
Assuming you're not here just to troll (though your original choice of thread title makes me wonder.....), a suggestion that might (or might not) help.
For what it's worth, I can load projects created under Sonar 8.x.x and X1 into X2 without problems. If there was a general/widespread problem loading pre-X2 projects into X2 without X2 crashing I suspect this forum would be alive with it. It isn't.
You say you're running Sonar 64bit, but in only 4GB of Ram. I'm wondering if that's enough for what you're doing. Multiple instances of Dim Pro can use lots of RAM, depending on the sounds loaded. Some Session Drummer kits use loads of RAM as well. DAWs do not like being in an environment where they are squeezed for resources.
I ran X1 in 4GB without problems, but apart from Session Drummer I use hardware synths so I don't usually have synths or large sample libraries filling up RAM.
I suggest getting Windows Task Manager or the resource monitor up and running and see how much RAM your're actually using as you load multiple Dim Pros/whatever.