When trying to add a new site, I get the following error:

500 - An error has occurred.
Unable to load Database Driver:

Return to Control Panel

I have no idea where to even start

Thanks.

I completely uninstalled the component, and reinstalled...

Joomla 2.5.1
JMS 1.2.75

Do you use a special driver other than MySQL and MySQLi ?

I am also getting the same error after upgrading to joomla 2.5. In the server > database settings it doesn't even give you an option to choose a database. The only option in the drop down is "none". This is on my master as well as all my slaves

Same Problem, but only on the general management of JMS

/index.php?option=com_multisites&task=manage : Unable to load Database Driver:

/index.php?option=com_multisites&task=templates : ok
/index.php?option=com_multisites&task=tools : ok
/index.php?option=com_multisites&task=checkpatches : ok
... : ok

Concerning the "drop down" is "none", which version of JMS do you use ?
If you use JMS 1.2.74 or 1.2.75 we had a bug introduced in 1.2.74 that is fixed in 1.2.76.

Concerning the problem of the "unable to load the DB driver", the only answer that I know for that is that you have a wrong DB connection somewhere.
Perhaps this is in a slave site that has a wrong value.
In the manage site, to compute the "refresh icon", JMS connect on each slave site DB to count the tables. Perhaps you have a slave site with the wrong value.
You can try disable the "refresh icon" to see if you still have the problem.
You can do that in the "/adminsitrator/component/com_multisites/multisites.cfg.php" file that you can edit and remove the comment concerning the
define( 'MULTISITES_REFRESH_DISABLED', true);

Hi Edwin

The problem is FIX when the "refresh icon" is disable.

You can do that in the "/adminsitrator/component/com_multisites/multisites.cfg.php" file that you can edit and remove the comment concerning the
define( 'MULTISITES_REFRESH_DISABLED', true);

I think that the problem come from the New Joomla 2.5 that have multiple news DB.

Or cause i create manualy Views in DB.

Thanks.