Fatal error while upgrading

Question

While upgrading from 4.5.8 to 4.6.3 on a Drupal site, the upgrade script stuck and when I refreshed, i got

Fatal error: Cannot redeclare class CRM_Core_ClassLoader in
[MYSITE]/sites/all/modules/civicrm/CRM/Core/ClassLoader.php on line 36

Now I can't even log into the backend of my site.

Answer 1

Can you ensure that you do not have two copies of the civicrm codebase (irrespective of what you might have renamed it to) under

[MYSITE]/

Most likely the error is caused by php finding two copies of the CRM/Core/ClassLoader.php file