if you are getting a dialogue box saying that you are not eligible to register then you must have eaten missed the round of verification of documentsif y or there must be in a floor somewhere in your registration procedure of you must not of qualified the particular cut off listed down in NEET PG 

in order to clarify exactly you are not permitted to participate in the counselling I think you should mail your call at the helpline of the the Neet PG authorities given on the website to solve your purpose