Can't add moderators through forum manager
 

When trying to add a moderator to a forum we get this message:

Fatal error: Could not open [path]/includes/xml/bitfield_vbulletin.xml in [path]/includes/class_bitfield_builder.php on line 130
#0 vb_error_handler(256, Could not open /srv/customers/08191201/mediseedcollective.info/www/includes/xml/bitfield_vbulletin.xml, /srv/customers/08191201/mediseedcollective.info/www/includes/class_bitfield_builder.php, 130, Array ([layout] => ,[include_disabled] => ,[obj] => vB_Bitfield_Builder Object ([data] => Array (),[datastore] => Array (),[errors] => Array (),[datastore_total] => Array ()),[temp] => Array (),[handle] => Resource id #10,[file] => ,[matches] => Array ())) called at [(null):0] #1 trigger_error(Could not open /srv/customers/08191201/mediseedcollective.info/www/includes/xml/bitfield_vbulletin.xml, 256) called at [/srv/customers/08191201/mediseedcollective.info/www/includes/class_bitfield_builder.php:130] #2 vB_Bitfield_Builder::build() called at [/srv/customers/08191201/mediseedcollective.info/www/admincp/moderator.php:67]


I have also seen this pop up while trying to do other tasks is this something easily fixed?I know one of our other admins has had problems and i will ask him to relay any error messages to me if this one doesn't tell us anything.I'm certainly no computer whiz but i can follow instructions and really want to have our forum running smoothly so i just need to get a few hints as to what to do.Is there a debug mode or a a way to find out exactly what needs fixing?
I appreciate any help :)