In order to fix this execute the following commands:
# sudo su cyrus
This will make you the cyrus user.
Now execute
# squatter
This will index all your e-mails (more info by executing $ man squatter). This index is not incremental so you need to run this task once in a while. It might be usefull to create a cronjob for this command.
quelle:http://basvandijk.eu/2010/08/09/fixing-the-cyrus-mailserver-squat-failed-error/