fail to join party is Blacklist?

[LilithThanheim]

or that you don't match the job or iLVL they are looking for.
Many possibilities. Could also maybe be someone in the group has you BL or you have them BL. Would that prevent the join up if such were the case?

If you have someone blacklisted in the party (save for the party owner) you can still join, though I am unsure if you can join a PF if someone in the party has you blacklisted (other than the party lead, of course).