Hey guys. Thank you very much for checking it out for me. After once again double checking everything, I have found that all the old accounts can’t post the comments properly (I would imagine something got corrupted in the DB or elsewhere) and all the fresh accounts post without any problems. Therefore, it seems that the problem was/is on my end. Sorry for the hassle and thank you for your support. Case resolved.
P.S.> Thank you for the best free WP comment plugin. Waiting for the premium version.
