smb.conf file
guest account = chris
if 'chris' belongs to only ONE group a core dump on start up is
very likely.  I believe the core dump happens in the qsort function
which is in the remove_duplicate_gids functions.  It appears that the
qsort was sorting 'space junk' for the last entry.

If one looks at the logs, they are reporting one too many gids.

"remove_duplicate_gids: Enter 3 gids" even if there are only 2

My temporary fix in file system_smbd.c:

*grpcnt = ret;   // was  *grpcnt = ret + 1;

this is actually very similar to 
http://samba.org/ftp/unpacked/junkcode/getgrouplist.c


Hope this helps.