GeorgiosT if your site has been customized, you should be careful when upgrading. It will overwrite all changes you made so far. You should setup a development site to test before uploading anything to LIVE. If you can't fix the issue, please send us ticket.
I installed it at SocialPublisher 1.2 again the same
will not be compatible with mooSocial 2.6.2
I do not know what else is wrong