Hello,
I wanted to test k2, so I installed a fresh Joomla! 2.5.4 unde XAMPP, and then installed the K2 via Extensions Manager.
Right after the installation completed, I could see these lines all over my Joomla! backend:

If I acces K2 under the Components menu, I get to see a lot of those lines.

What is really going on?

Solved:
- set display error to zero or Off in php.ini under XAMPP.

It's a php thing search the official joomla forums. There is something you have to add/edit in the php.ini file, or else you will get this with every local website you make.