Symptoms
Office 365 synchronization script fails with the following error:
User with login 'user1@domain.tld' already exists.
The following entries are present in the synchronization log:
2013-09-09 15:51:08,723 DEBUG Subscription <SUB_ID>: going to add new user with login 'user1@domain.tld'
2013-09-09 15:51:09,465 ERROR Subscription <SUB_ID>: error by updating: Error during OpenAPI call: User with login 'user1@domain.tld' already exists.
Cause
This issue is caused by the fact that a task to create this user was previously canceled. The entries in the POA database were created, however, MOSI Gateway DB was not changed. Check the canceled tasks for tasks in queue aps_application_instance[O365_INSTANCE_ID] and word 'user'.
Resolution
Find and process the canceled tasks related to the user in question.
Also, check if such user name is already in use under another account:
PCP > BA > System > Users