User cannot receive mail: "Cant create user file"

Starting a few days ago, one of our users could not receive emails anymore. Everything is being bounced with the following type of message in /var/log/mail.log :

Dec 3 12:35:31 uk3hosting postfix/local[14201]: 6909D9ACEB7: to=, orig_to=, relay=local, delay=9, status=bounced (can't create user output file)

I have done some reading around and it seems that this could be a problem with procmail and/or permissions? I am confused though because only this one user is having the problem. All other users on all virtual hosts are fine, including other users on the same domain. I have checked and this user is way below quota.

heres the result of "postconf -n" :
----------------------------------------------

alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
append_dot_mydomain = no
biff = no
broken_sasl_auth_clients = yes
config_directory = /etc/postfix
header_checks = regexp:/etc/postfix/header_checks
home_mailbox = Maildir/
inet_interfaces = 127.0.0.1, 83.170.85.83
mailbox_command = /usr/bin/procmail-wrapper -o -a $DOMAIN -d $LOGNAME
mailbox_size_limit = 0
mydestination = localhost.localdomain, localhost.com, localhost
myhostname = uk3hosting.cfmhosting.com
mynetworks = 127.0.0.0/8
myorigin = /etc/mailname
recipient_delimiter = +
smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
smtpd_recipient_restrictions = permit_mynetworks permit_sasl_authenticated reject_unauth_destination
smtpd_sasl_auth_enable = yes
smtpd_sasl_local_domain = $myhostname
smtpd_sasl_security_options = noanonymous
virtual_alias_maps = hash:/etc/postfix/virtual, hash:/var/lib/mailman/data/virtual-mailman

and heres "/etc/procmailrc" :
------------------------------------------

LOGFILE=/var/log/procmail.log
TRAP=/etc/webmin/virtual-server/procmail-logger.pl
:0wi
VIRTUALMIN=|/etc/webmin/virtual-server/lookup-domain.pl $LOGNAME
:0
* ?/usr/bin/test "$VIRTUALMIN" != "" -a "$VIRTUALMIN" = "11829477095661"
{
INCLUDERC=/etc/webmin/virtual-server/procmail/$VIRTUALMIN
}
DEFAULT=$HOME/Maildir/
ORGMAIL=$HOME/Maildir/
:0
* ^X-Spam-Status: Yes
/dev/null
DROPPRIVS=yes
:0
$DEFAULT

Status: 
Closed (fixed)