how to convert a shared mailbox back to normal - Microsoft Exchange

At some point in time you may be required to convert an exchange mailbox from a shared mailbox back to a normal mailbox.

It should be as simple as set-Mailbox -Identity [mailboxname] -type regular

However,I got the following error (See above)

Error on proxy command 
Active Directory operation failed on [DC name] The value provided for the new password does not meet the length and complexity requirements

As we know a shared mailbox is usually disabled and no password set.

Solution

Simply set a password for the mailbox in Active Directory and run the command again.