[imp] pgp problem,help

[alex]

Hi all: 
I like pgp function,but till today it still can not work in our office. 
Every user have two contact lists in turba in my site,one is mysql backend for private used and the other one is ldap backend (read only,public).
The ldap contact also is authenticate backend. Everytime when i tried to sendmail a mail to one of the ldap user with pgp-encript.I got 
  PGP Error: More than 1 entry returned.
  Message sent successfully.
OR
<STRONG>More than 1 entry returned.</STRONG>
I think ,because the same mail-address entry exist in both contact lists.so cause such problem,right ?
If true,how to fix it ? or i miss something forgot setup ?
Alex