Zarafa 7.0.5-31880

This error occurs ...
... when I send invites from a public calendar
... seems if i send invites and "always_send_delegates = yes" (maybe if I have send-as rights, too)
... maybe under other circumstances

Is there a workaround?
Working with Outlook is not possible because of Linux and Mac-Clients.

regards Kim

/Edit:
But this happens only sometimes.
I removed my From-Adresses, set always_send_delegates=no, restarted spooler and server
set always_send_delegates=yes, restarted spooler and server, set From-Adresses -> it worked
... very strange