First of all, and most importantly, invalid references are warnings and as such should not prevent you from launching the application. If you cannot launch the reason is somewhere else, and if no other validation appears, have a look at the tersus.log file.
I'm not totally surprised that new warnings appeared with 2.1.18, since we've discovered some bugs in the validation logic, failing to identify certain cases, and fixed them, since 2.1.15 (see the change log @ http://www.tersus.com/#Id=210).
Of course, when fixing bugs it is possible to introduced new ones, causing certain legitimate references to be identified as invalid. We are actually aware (and have fixed) a case where unused models which include invalid references are the cause, where previously such cases were ignored, and this might be the cause of the warnings you've encountered.A fix for this will be included in 2.1.19.
For best results, use the Firefox browser..