Recently I assisted a client to migrate to Office 356. They had decided to move their own data. They setup the new mailboxes and then attempted importing the PST’s from old mailboxes. During that process, we added additional Distribution lists and members. The client could locate it on the web portal but was not able to see it in Outlook. When they decided to download the Address book, they
received an error downloading the address book.
Then we tried running a “Send and Receive“. We then received an error as well.
This error means that the address book is in use and not able to update. In order to resolve this. Close Outlook. The go to the following location: C:\Users\<Profile>\AppData\Local\Microsoft\Outlook\Offline Address Books
Create a backup folder and move the address books into the folder. the folder “Offline Address Books” should only have the backup folder. Then reopen Outlook and it should then re-download the Address Book. This will download the updated Address Book.