[TxMt] Latex: Project Settinsgs, TM_LATEX_MASTER, ??? error message

[Flo]

Hi,
I've got a problem..

Using the instructions from the manual and from the mailing list, I  
hit the Info-button in my project drawer (without having any file  
selected) and set the
TM_LATEX_MASTER to
> /Users/flo/Desktop/DiplomArbeit/070627_da_draft01/da_draft01.tex

 From now on, whenever I hit "Typeset and Preview" I get the  
following error in my Preview-WIndow:
> Error locating external viewer: ‘/Users/flo/Desktop/DiplomArbeit/ 
> 070627_da_draft01/da_draft01.tex’

I've tried saving my masterfile "da_draft..." as relative and  
absolute path, but both showed the same error.

In my external viewer, PDFView everything is fine and gets properly  
compiled.

Why is this so? And is there something I do wrong? Anyway to fix this?
Thanks

Flo