fatal erros plg_hikashopusergroup

That error is in the plugin: extensions.4u2.co.il/hikasop-user-group-ftw
Please note that we are not the ones developing that plugin but a third party developer:
extensions.4u2.co.il/hikasop-user-group-ftw

Also please note that if you're trying to use that plugin by itself it won't work as it needs HikaShop and that this plugin does not currently work on Joomla 3.0 (which could explain that error).

You could try to add the line:
jimport('joomla.html.parameter');

just before the line of that error to fix the problem.

Please note that we are not the ones developing that plugin but a third party developer. Please contact him for hep related to that plugin.

These notices can be removed by setting the option "error reporting" to "none" in the configuration of joomla.