White screen on admin - main menu --> click on Home to adjust title

Hi all,

I am willing to edit the main menu content but when i try to click the home button in main menu i get a white screen?

Also when i try to add a menu option i get a blank screen?

So shortly: White screen on admin - main menu --> when i click on Home to adjust title "welcome on frontpage" and also when i try to add a menu button!

It;s o this link e.g.:
administrator/index.php?option=com_menus&menutype=mainmenu&task=edit&cid[]=1

Any ideas why this happens?

Thank you!

Anyone?