WARNING: GeneratingMailbox is null; this OAB will not be generated until GeneratingMailbox is set to an arbitration mailbox with OABGen capability.

The above error is may be common to you or you may have seen that creating offline address book but if notice it says address list already matching the identity “Marketing” where I’m trying to add marketing to the new OAB, so what is going wrong here?

When I looked up the newly created Address List (as mentioned above) and the GAL , I found out that GAL is also named as Marketing, see below

As soon as I renamed it

I’m able to create a new OAB