I'm just sitting at KPIE St Petersburg Clearwater airport, not touching anything and there it goes! Module atc.dll. Was that dll replaced in ver 9.1?Owen

Oh oh, joys of spring and summer :)

I assume you have no add-ons then, no traffic updates, AFCAD updates, etc? 9.1 won't stop CTD's caused by add-ons, so I always suggest looking there first. Given your error, I would look at any traffic or AFCAD changes you've made. Also note that a scenery change in Texas could cause a crash in Clearwater if you have an add-on file gone bad.-John