Recently we came across quite a weird issue. The administrators say that once in a while they notice that user accounts in MS Dynamics CRM are lost .

When a new user is added to the system, the administrators add him/her to the Active Directory first. Then, they go to Dynamics CRM interface, then to system configuration -> administration -> users and add the new user to the CRM, add roles to this user, grant them relevant permissions. Then the user is able to use a custom application, which connects to the Dynamics CRM via WCF.

After a while (few weeks or months) the user is unable to use the custom application because Dynamics CRM cannot authorise this user. When administrators open the Dynamics CRM user management interface (configuration -> administration -> users ) and browse through the list of CRM users they cannot find the user in the list. When they try to add the user to Dynamics CRM back, the CRM fails with the error message "User already exists". Moreover, the user still exists in the Active Directory.

The admins are very sure the user had been added to the CRM before he/she started to work. The only fact the the user was able to use the custom application normally says that the user had been indeed registered in the CRM. How come the user is not listed in the CRM user management interface at all?

Have anyone faced any issues like that? Seen or heard of disappearing CRM users somewhere?

Any help is appreciated. Where can one start digging?