[exim] bad group for .forward

I got this error:

2005-01-24 11:23:22 1Ct0xz-0006Tq-Cm == yyyyyyy@???
R=userforward defer (-1): bad group for /home/yyyyyyy/.forward

the only difference for this user is that .forward has permissions
-rw-r--r-- and owner yyyyyyy:groupname

(on that host the users do not have an individual group, so most
users have just group "students" number 102 )
whre is the error [this occurred after i upgraded from 3.3 to 3.4 .
users with normal "personal"gropup works fine.
I tried also to give to password a random gropup, without success).
without .forward mail is delivered correctly.

PS: about mi previous posts on pine timeout problems: it was a
misconfigured nis server ! now it works fine.

--
Leonardo Boselli
Nucleo informatico e Telematico
Dipartimento Ingegneria Civile
Universita` di Firenze
Via Santa Marta 3
I-50139 Firenze
+39 055-4796-431
+39 348-8605-348
fax 055-495-333