Load balancing failed to find a valid mailbox database.
We run no load-balancing, so what does this mean?
Data Recovery Berkshire
using Get-MailboxDatabase | FT Name, IsExcludedfromProvisioning, IsSuspendedFromProvisioning we found the DB name and then using
Set-MailboxDatabase "MailboxDatabaseName" -IsExcludedFromProvisioning $false we set it back to false and created the user without a problem.