Expert Trainer Cavalier class feature not recognized in the prerequisite system, making it impossible to pick an Archetype that modifies it or the Horse Master feat.
Looking at the Horse Master feat, it appears this issue was already fixed for 6.03.01. You can grab 6.03.1 to give it a test, if you would like. Normally I'd send you a fixed file, but if you're running 6.02.1 then I'd end up causing you more issue as the entire system got updated. Easier to upgrade to 6.03.1 and get all the updates that way.
Which archetypes are you specifically mentioning though? That would help to make sure the issue is corrected completely for you.
No reply from OP, appears to have been addressed. Closing.