sudden error message after back up button press at admin panel

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Many thanks to forum visitors..
I have problems with display of my website.

I did not know the accurate knowledge about PHP or DB so on..
So, I used this concrete5 CMS system..

my website http://www.thejamong.com
If i press the top button named as portfolio, below message is displayed..

Whoops \ Exception \ ErrorException (E_ERROR)
Call to a member function getRootTreeNodeObject() on a non-object


Please let me know some solution..Please

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