You can only export lower than 3.0 if your the version allows it. You can't for example have a vertical with "No B-layer" selected and export it as a 2.5, it must be at least 3.0.
All the verticals must be 1,5 in order for the production tool to export a 1.5 mib. If you go into to production tool you will be able to select vertical and then in the info window up in the right see what mib version it has.
Let me know how it works out!