URGENT: help with mail error

[ohmadevo]

A client is suddenly unable to send/receive email and I get an error when I try to access the client's email within Plesk. Can someone please tell me what it means and what I can do to fix it? It *just* happened.

Error: Unable update mailbox: mailmng failed: mailmng: Unable to open file "/usr/local/psa/var/lock/files/05a614fac33d3831305fdb55b2be8e8a": Permission denied.
System error 13: Permission denied
mailmng: Error occurred while locking the file /var/qmail/users/poppasswd: Permission denied

System error 13: Permission denied
mailmng: Unable to remove record from popasswd file

System error 13: Permission denied
mailmng: Unable to open file "/usr/local/psa/var/lock/files/05a614fac33d3831305fdb55b2be8e8a": Permission denied.
System error 13: Permission denied
mailmng: Error occurred while locking the file /var/qmail/users/poppasswd: Permission denied

System error 13: Permission denied
mailmng: Unable to add record to poppasswd file
System error 13: Permission denied