[Dovecot] failed with uid Permission denied

[Rein Laaneser]

Hi
Does somebody know the workaround
I have some users, who are able to log in to dovecot but others not.... 
even the failpermissions in directories are same. Also mbox folder is 
excatly same  mail

Some settings in /etc/dovecot.conf 

first_valid_uid =  500
last_valid_uid =  1500
first_valid_gid = 500
last_valid_gid = 515

default_mail_env = mbox:~/mail:INBOX=/var/spool/mail/%u

So the "someuser" is able to log in but "testuser" not
log from testuser logging in  

somehost imap-login: Login: testuser [193.x.x.x]
somehost dovecot: chdir(/home/guest/testuser) failed with uid 893: 
Permission denied
somehost dovecot: child 8729 (imap) returned error 89

Any idea???