Hello
I solved this this morning by running (as root)
/usr/local/psa/bootstrapper/pp11.5.30-bootstrapper/bootstrapper.sh repair
And then for a domain that continued the same, went to the panel, to the domain hosting configuration, and simply applying it (without change anything).
Hope helps
UPDATE: Well, i readed to fast! This happened me with the domain's web, not webmail, but hope helps anyway.