I have found a strange work-around which has solved my current problem.
I seems like add web reference wizard don’t like multiplicity on the first child record, if the multiplicity is placed on the element. When i move the multiplicity one level up in the xsd-dile to the actual sequence-tag, the problem disapeaers.
Since i ony have one record in my sequence this dosent bother me to move the multiplicity. But i can se a problem when more than one record is in the sequence