Well the solution was kind of wierd.
If you execute the script in SSMS and the query has errors you can double click the error line and the faulty command is highlighted. Due to this I did my research at the wrong place and a collegue of mine located the error in completely other table, which really had a default value and a default binding.

Conclusion:
Don't rely on this double click feature from SSMS.

>>Problem SOLVED!!!
>
>And the solution was ..... ?
>
>~~Bonnie