It sounds like you have a rowsource that's too big. Check out this MSKB article that addresses the subject:

PRB: Mismatched Pushjmp/Popjmp Call Message from Modify Form

>Hi,
> When i type 'modi form c:\project...\conv' to modify the form, the sysetm appear a messagebox and written as 'mismatched pushjmp/popjmp call', and i choose 'OK', then the Visual Foxpro automatically quit.
>
> How can i modify this again, because this form is very important to me, pls help, thank you!
>
>
> Aston