However - I found a way to work around the problem. There is a lookup column in my sharepoint list which refers to a document library. This lookup column prooved to be the troublemaker. The workaround is to create a list view that does not contain the lookup column an refer to this viewGUID. With that "de-troubled" view everything works fine.
It would be interesting if anybody has solved the problem of loading the content of a lookup column as such. To me it seems reasonable enough to load both sources an let qlikview do the lookup.