We have exactly the same problem, but it doesn´t only occur for jabber profiles like described, it occurs for phones too.
Whenever the DN already existed before in the system and is not a completely new one, the error occurs. For example if you hover over the i symbol of an existing line and select "Change" for example to change the pickup group or just the line description the error occurs when pressing "Continue".
The only way we can create phones and jabber profiles with a line without getting this error, is when the DN was never associated to any user in the system.
The prime is pretty much useless for us with this error. We are now running Version 12.4.1588 and already had this problem with a early version of 11.x. Please fix this soon!
