flist:_Permission_denied

Previously I got the Smartlist to work on this RH linux box.

Today it quit working, nothing recorded in list log but this error in 
/var/log/maillog:

Aug 25 17:21:30 neo qmail: 1251238890.973347 delivery 128: deferral: 
/bin/sh:_/var/list/.bin/flist:_Permission_denied/

The only thing I did during this time was to add 'r' permission for the 
web server to one of the list dir, but wonder why mail to any other list 
address and -request addresses all got this "permission" problem.  I 
looked at file/folder permissions and don't see anything odd. e.g.:
drwxr-sr-x 2 slist slist 4096 Aug 24 10:16 ~list/.bin
-rwxr-xr-x 5 slist slist  25K Jan 18  2007 ~list/.bin/flist
drwxr-sr-x 3 slist slist 4096 Aug 24 13:35 ~list/mylist
etc.

Any hint what could be wrong?

Zhiliang