I think this problem may cause in two reasons.
1 .Cisco CallManager Automated Attendant cannot find a user that a caller specifies when dialing by name. The extension of the requested user is not valid because the user does not have a primary extension assigned in Cisco CallManager, or the ccndir.ini file is missing information.
2. It might be due to the fact that the ccndir.ini file is missing information or the extension is not valid because the user does not have a primary extension that was assigned in Cisco CallManager Administration
To resolve the problem
1. Verify that the user has an entry in the Cisco CallManager AA Name dialing field and that the User record has an associated phone and that the primary extension button is chosen.
2. Verify that the ccndir.ini file contains the following lines:
USERBASE "ou=Users, o=cisco.com"
PROFILEBASE "ou=profiles, ou=CCN, o=cisco.com"
3. If you migrated Cisco CallManager from Version 2.4, a possible schema issue exists. In LDAP Directory Administration, verify that the user Owner field is in Userid format, not fullname format.
For further information click this link.
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/admin/3_3_2/ccmfeat/fsAppB.html#wp1012431