Hi Dino,
OK, so the ForDon.rpt and ForDon2.rpt have saved data but in both the subreport is OnDemand, so I can't test it.
for the f.rpt report I can page back and forth in the same order you do and no problems for me.
Can you run debugdiag and analyze it and see what it tells you when the crash happens?
I think I found the cause... upgrade to SP 14. You are still using SP 10:
There was a memory leak in that build that was fixed in SP 12...
Don