I have been having a problem in GP that when I change Omnisphere presets, GP would crash constantly. I sent in a crash report and GP tech immediately narrowed it down to Omnisphere. This is crashing inside Omnisphere when Gig Performer is loading the plugin. It seems to want to load a sound bank (FXBFile) and the crash is occurring inside Omnisphere during that process.
Spectrasonics knows about this problem and sent me an Omnisphere install fix which will be released soon as a general update.