This error stems from the fact that in php 5.3.0 the function ereg () deprecated.
There are two quick solution to this problem:
1. Go to an earlier version of PHP (this can be done through the hosting control panel, or writing a letter asking to move to a more earlier version of PHP allows a service to your hosting company)
2. Edit the source file in Drupal. To do this, open the file in the editor /includes/file.inc and find there the following line
