I’m with A2Hosting too.
First of all, i rarely have any issues with them so it’s not a big deal that this came up. I was still able to access my admin page by going to a post and clicking on “edit” then navigating to where i wanted.
A2 Hosting upgraded their servers yesterday to allow a choice of php versions. Evidently the new default PHP version is not entirely compatible with WordPress.
The new default PHP Version is 5.2.9 Cached, which is what caused the error message. After changing it to the second option: 5.2.9 Zend Optimizer” the error went away.
To change your version, go here: CPanel -> Software/Services -> PHP Version -> 5.2.9 Zend Optimizer