After updating Joomla version “Media Manager” in Administrator panel not working-Collection of common programming errors

If you don’t have a backup of your previous site before the upgrade, Im afraid reverting won’t be possible else extremely hard and time consuming. Take a backup of the current website you have and try upgrading to Joomla 2.5, using jUpgrade.

I explained on this Stackoverflow post, why it is important to ensure your Joomla version is up to date.

Why should I keep my Joomla version up to date?

Once done, check if the Media Manager is working.

Hope this helps