PHP Fatal error: Class 'sfPropelRouteCollection' not found

[cinilak]

I get a 500 error when I try to run the site's backend in IE.

The error from title gets generated in apache error log.

I tried investigating config_routing.yml.php and it appears that it's calling a new sfPropelRouteCollection class, and cannot find it.

I found the file containing it in: \lib\vendors\symfony\lib\plugins\sfPropelPlugin\lib\routing\sfPropelRouteCollection.class.php

I cleared the cache several times, that didn't help.

The frontend of the site is running normally

I understand that some of you might think that this should go into plugins section of this forum, but I thought that this is probably more related to how symfony works, rather than the plugin itself.