Xilinx 6.2sp3: Post Place and Route Modelsim6.0 Simulation Crashes

I am trying to simulate a Xilinx design with Rocket IO smartmodel. I use the Modelsim from within the ISE Project Navigator. I can perform a functional simulation ok but when I try to do a Post Place and Route Simulation, Modelsim crashes. I can see all the libraries loading properly : the Swiftpli.dll and the simprims etc.... but after it loads the glbl.v file, it crashes (or at least, that is the last thing i can observe before the Modelsim Window vanishes) I have modified the modelsim.ini file as suggested on the Xilinx Answer Database, have compiled all the libraries as recommended. Any ideas about the possible causes for such a crash ? Thanks, Adarsh