>SCAN
>replace modacad.mochk009 WITH result.mochk009 for result.mainkey=modacad.mainkey
>ENDSCAN

>I basically want to change modacad.mochk009 (table) with the value in the cursor (result)
>where the mainkey is both in modacad and result.

For that to work as you have it, you would need a relation set between them, which you don't mention here.

If you do have one, and it's set correctly, try:

REPLACE mochk009 WITH result.mochk009 IN modacad FOR result.mainkey=modacad.mainkey

in case you're having trouble with one of your tables being at EOF().