I had this problem is 9.3. The reason why this problem exists as far as I know, is that if you try to create a feature, ArcGIS Mobile tries to create the attributes immediately. If the domains (coded) don't have a default value, it won't make a new record in the table. Thus you will get an error.
I have 2 coded domains and one range domain, the coded ones I had to make a default, and so I made it "none" which is an option in the selection. For the range domain you can leave that empty with no default.