It could be timing issue. Try this

_CLIPTEXT = "MESSAGEBOX('TEST')" && Command to paste
MODIFY COMMAND myprog NOWAIT && Open a program file
DOEVENTS 
ACTIVATE WINDOW "myprog.prg"
SYS(1500, '_MED_PASTE', '_MEDIT') && Paste menu item 

>Thanks, Sergey. It's working now. Oh, I hate that!
>
>>Jeff,
>>
>>Try

_CLIPTEXT = "MESSAGEBOX('TEST')" && Command to paste
>>MODIFY COMMAND myprog NOWAIT && Open a program file
>>DOEVENTS
>>SYS(1500, '_MED_PASTE', '_MEDIT') && Paste menu item
>>

>>>I've pasted the exact code in the help for sys(1500) and it doesn't work for me - there's no text pasted in. Doesn't work in VFP7 or VFP9 in developer version of VFP or as an EXE.
>>>
>>>From VFP9 Help (and is the same in VFP7):
>>>pre>
>>>_CLIPTEXT = "MESSAGEBOX('TEST')" && Command to paste
>>>MODIFY COMMAND myprog NOWAIT && Open a program file
>>>SYS(1500, '_MED_PASTE', '_MEDIT') && Paste menu item
>>