Symptoms

When trying to add a user using the AD Create method, it Gives an
"Exception has been thrown by the target of an invocation."
Then if you try add the user again it says
"User XYZ already exists"
 

Diagnoses

We found that the Service account didnt have Account Operators rights and Multi Domain configuration was also incorrect.

 

Resolution

Corrected Multi domain configuration, added Roleinit and LDAP in the AD Service instance and removed what wasnt needed.

Also added the service account to the Account Operators Domain Group - This resolved the issues the client was having.