Yes this error
couldn't rename bogus "/var/spool/mail/web1_xxxx" into "/var/spool/mail/BOGUS.web1_xxxx.LHwI"
is gone but it's still not possible to login webmail with the info account.
Now the owner of the other email account is back from holidays and with his account login in is no problem
Do you think it's possible that we have saved too much emails (about 3500 very small sizes) and that out that exporting of the mails and recreating the account is the best way to solve this problem?