I think the problem he's having is that the slur won't end on the 2nd grace note, because of the way slurs behave in NWC. That is, a slur which starts on a regular note must end on a regular note; a slur that starts on a grace note must end on a grace note.
The solution is to use the Slur.ms object:
!NoteWorthyComposerClip(2.751,Single)
|User|Slur.ms|Pos:-6|Span:3
|Note|Dur:4th|Pos:-5
|Note|Dur:16th,Grace|Pos:-4|Opts:Stem=Up,Beam=First
|Note|Dur:16th,Grace|Pos:-5|Opts:Stem=Up,Beam=End
|Note|Dur:16th,Slur|Pos:-6|Opts:Stem=Up,Beam=First
|Note|Dur:16th|Pos:-7|Opts:Stem=Up,Beam
|Note|Dur:16th,Slur|Pos:-8|Opts:Stem=Up,Beam
|Note|Dur:16th|Pos:-7|Opts:Stem=Up,Beam=End
!NoteWorthyComposerClip-End