PFIM 4.0 for trial optimization - frozen screen

Hi everyone, I was wondering if anyone else has been having trouble using PFIM 4.0 lately. I've been experiencing a frozen screen when I tried to execute a simple 1 cmt model, actually an example from their manual. All functions including graph only result in a frozen screen. I tried re-installing and that did not result in any success. I definitely used PFIM successfully on a past project, a couple of years ago, on the same computer. Not sure what could be the issue! Any suggestions would be appreciated. Thanks in advance, Lisa