I tried making a new gsim file using the 'new' 3.0 Alpha, and (a) nothing showed up on the screen and (b) now it's not even opening (it crashes when I try opening the program). Granted I have been out of practice and I haven't actually used the Alpha before, so I may have done something wrong.  
 
I've attached the file, can anyone tell me what's wrong with it so I can fix it?

Yeah, I did that and eventually got something working again... but can I salvage the file I attached? Or do I just have to go back and make it all over again?

When  I open Mal's file I get a lot of "#QNAN" where actually positions and velocities should be .  I'm afraid the file is corrupt .

yeah, sorry.  there's no way I can recover it without the r & v's  

I'm not sure Mal , but my best guess is something happened at the input of your bodies . In C++ the Qnan stands for "not a number " . I also notice in the file  the value "#INF" , which probably is an infinite value . It may be possible you've tried to input a character instead of a value , which confused GravSim . Not sure as I said . Maybe Tony can explain how inappropriate input values are handled n the input section .  
I remember I once had  ,  a long while ago , a problem inputting values resulting in GravSim not starting . AFAIR I had problems choosing the decimal point versus comma .