I'll redo the installation again. I did do a full integration with vBulletin from the start, my users only disappeared after I did a db scan and repaired some broken users and comments, and the medium image size dimension rebuild.
The registration has never worked properly, since it was supposed to be integrated with vbulletin it should have used the vbenhanced templates but some were missing when the register link was pressed. Moving some Coppa templates from the template dir to the vbenhanced dir seemed to fix this issue though. But they wern't in the download of Photopost Pro.. :S