Found the source of the problem.
It looks like Qlikview server can not write to my Q:\
Q: \ = a shared folder on the same server (= D:\Qlikview)
Store Data into D:\Qlikview\Stores\Date.qvd
Store Data into \\Servername\Qlikview\Stores\Data.qvd
Both seems to work but when I want to use my shared folder to read or write using the Qlikview server it give a script error. Anybody knows why and how to get this to work?