Weird Error Message Above Header

[Hwona]

Sorry to bug again, but there's some strange error message above the header of my site:
Strict Standards: Declaration of File::getBasename() should be compatible with SplFileInfo::getBasename($suffix = NULL) in /home/wallie12/public_html/classes/class_file.php on line 19

Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /home/wallie12/public_html/classes/class_file.php:19) in /home/wallie12/public_html/classes/class_session.php on line 13

And above the ACP:
Strict Standards: Declaration of File::getBasename() should be compatible with SplFileInfo::getBasename($suffix = NULL) in /home/wallie12/public_html/classes/class_file.php on line 19

Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /home/wallie12/public_html/classes/class_file.php:19) in /home/wallie12/public_html/classes/class_session.php on line 13

Strict Standards: Declaration of AdminSidebar::setDivision() should be compatible with Sidebar::setDivision(GUIComponent $module) in /home/wallie12/public_html/classes/class_adminsidebar.php on line 16

The funny thing is, I never had this issue until this morning, and I don't remember editing any files after last night. Can someone help? I'm also noticing this on a LOT of other sites - particularly on x10.

Edit: And now, I can't log out. O.o