Please see the image, I got the error just shortly after I upgraded Joomla 2.5 website to Joomla 3.4.4
This will really be a great help for me anyone can help.
You may have some extensions that are not compatible with Joomla 3.x.
If you can still log in to the back-end, try disabling or removing these to see if it helps.
This error generally arises because of mismatch in columns present in Joomla3x and Joomla2.5 tables. To fix this, follow the following steps:
1) If you can access administrator section, then click on the Extension Manager > Database tab > Click Fix button.
2) If you cannot access the Database view in admin, then achieve the above step by entering in the URL:
--This will fix all the database warnings and errors.
If this also doesn't work for you then try updating from scratch.
Hope this helps.