Please help! gaming mag temp 3.0

Fatal error: JApplicationCms::getUserState() [<a href='japplicationcms.getuserstate'>japplicationcms.getuserstate</a>]: The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition &quot;Joomla\Registry\Registry&quot; of the object you are trying to operate on was loaded _before_ unserialize() gets called or provide a __autoload() function to load the class definition in /home/impenetr/public_html/Home/libraries/cms/application/cms.php on line 513 when I try to install I get this

This is core Joomla error and it comes from Joomla files and this means that something is wrong with Joomla. When you switch to Prostar template you will get the same error?