hmmm just a shot in the dark, but here goes...

Maybe when you call the VB app from VFP, VFP goes immediately to the next line of code, without waiting for the VB app to finish executing, e.g.

   02 ' some code
   03 VFP_Code_To_Launch_App VBApp.exe
   04 Read_File_Made_By_VBApp.exe
   05 ' some code

After executing line 03, line 04 is immediately executed, whether the file has been created already or not (Windows multitasking at work...?)

Try putting some sort of delay between the 2 lines and see if it solves the problem. I seem to remember a VB trick to force VB to wait for the launched application terminate before continuing with the rest of the code, but I don't know if there is an equivalent for VFP

Hope this helps