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I can see the error you are referring to and i have one of our development team working on it right now. Either myself or the developer will contact you shortly. I am sorry for the frustration this has caused you.
I will oversee this to make sure we get to a fast resolution for you
This issue caused by this plugin XIUS Community Plugin, which not compatible with newest Jomsocial and newest Joomla version.. I already disabled it, and the error 500 is dissapear now.