1. mAvik Thumbnails 2.x doesn't work with Joomla 2.5, only Joomla 3.x. But you can use version 1.x for Joomla 2.5.
2. " Strict standards" is not error. It's only information for developers. You have to set Errors level: minimun (or none) in global settings of Joomla.
The administrator has disabled public write access.