One or more blueprints has an unresolved compiler error

One or more blueprints has an unresolved compiler error.
New to AI programming, not all that adept at BP’s anyway short of usual things, so I accidentally named ai_controller class, AI_controller though it was own bp. Did this mess something up ?

If I restart Ue4, I can play again with no errors, then I double click on say CONTENT/thirdpersonBP/BLueprints>thirdpersoncharacter , play and this:

I have a bunch of bp’s, upload, load and tons more, but I never did anything with them, I don’t have the programming knowledge TO do that, what is causing this ?

thx :0