Hmm, you sure you spelled it right? I just checked my Tandy manual and it would seem that Gosub and Return should work OK.

Oh wait, I see what it is: you don't have an END statement before the subroutine. If you don't have one then it will crash. I think... try it.

like this, line 160

160 END

Also remember that the RETURN sends it back to the line AFTER the GOSUB function gets called. You can do (for example) a RETURN 200, for example, to specify it to return to line 200, instead of the phrase right after GOSUB.