FB.dll is not part of Opus and is not something that Opus uses directly. It is probably part of a product that injects its DLLs into all other processes and is going wrong because that DLL isn't in the path.
One of these threads may help:
[ul][li]http://forums.autodesk.com/t5/Autodesk-Inventor/fb-dll-system-error/td-p/3277453[/li]
[li]http://forum.easeus.com/viewtopic.php?p=41718[/li]
[li]fb.dll error[/li][/ul]