Hi Mike,

Thanks for your post here on the Community forums.

As you said Error 194, can be triggered if you are using a glass and it is not included in the loaded glass catalogs under System Explorer > Material Catalogs > Catalogs to use. However, if this is the case, then you should get a pop-up message like the following:
 

If you add a catalog that contains the desired glass, then the error will go away.

If you didn’t get the pop-up message, please check your settings under the Project Preferences > Message Boxes:

I have checked with our developers, and error 194 doesn't appear to be attached to any particular core message, it can be triggered by different problems, which depend on the exact file and analyses used. I think this is the reason why error code 194 is not listed in the collection of error codes in the Help system under:
The Setup Tab > Diagnostics Group > OpticStudio Error Codes

Apologies for your inconveniences!

If you have any trouble with your files, please send it over to support@zemax.com, so that we can take a look and help in troubleshooting.

Best,
Csilla