Can you try upgrading to mojoPortal 2.3.9.6 and also download and install the very latest version of our Artisteer exporter from your user profile on this site. Also double check if you are using the very latest Artisteer (ie make sure you have Artisteer 4.1 not 4.1RC).
If you do those things and the problem remains then send me your .artx file so I can try to produce the problem on my machine joe dot audette at g mail dot com
Hope that helps,
Joe