Can't delete domain - ERROR: PleskFatalException

[gee_fin]

Trying to delete a domain (in fact two) I'm receiving this error -

ERROR: PleskFatalException
Unable to remove hosting: Unable to delete system user: SysUser->systemRemove() failed: usermng failed: usermng: Unable to set quota for user 'xxx'

0: /usr/local/psa/admin/plib/class.PhDomain.php:228
PhDomain->reset(integer '0', boolean true, boolean false)
1: /usr/local/psa/admin/plib/class.BsDomain.php:289
BsDomain->reset(integer '0')
2: /usr/local/psa/admin/plib/class.BsDomain.php:283
BsDomain->delete(integer '0')
3: /usr/local/psa/admin/plib/class.BsDomain.php:524
mdeleteDomains(array)
4: /usr/local/psa/admin/plib/class.Manager.php:351
Manager->removeDomains(array)
5: /usr/local/psa/admin/htdocs/domains/domains.php3:215

It's a bit annoying to say the least as I'd like to use the two domains as aliases, can anyone point me in the right direction on how to solve this?