Hi FCastro, that can happen if your installation has become corrupted or also if you're using a cracked version.

If it's due to your installation being messed up, please try downloading it again from here: http://moi3d.com/reinstall.htm

If you're not running a cracked version and you're still having problems after that please e-mail me at moi@moi3d.com with your license key so I can try to figure out what's going wrong.

- Michael