[quote="leo"]To fix this, double-click Opus_SetDllDirectory_Disable.reg registry setting in the attached zip.
[attachment=0]Opus_SetDllDirectory.zip[/attachment]
Important: After making the registry change, fully exit Opus and then restart it. (Don't just close all the Opus windows. Exit it completely as described in the linked post. If in doubt, reboot after applying the registry file.)
I've tested this with Autodesk Inventor LT 2013 and it made the menus work within Opus.
If you later want to restore things back to normal, use the other reg file in the zip.
The normal mode is more secure, but breaks a handful of 3rd party DLLs. It may make sense to complain to Autodesk that their code requires this unsafe mode to work, especially in software designed for viewing files which is inherently susceptible to binary planting attacks (info at binaryplanting.com).[/quote]
It works very good now. Many thanks for your help. 