When my users that are reseller admins try to create a new mail box they get errors. get error load balancing failed to find a valid mailbox database. there is only one database. this also happens when creating shared resource mailboxes. if i sign in as the main server admin i can create mailboxes because i can choose a database from the drop down. although as the main server admin i can not create resource mailboxes because a database drop down is not available.
This error message is actually coming from your Exchange environment. If you were to go into ECP and create a mailbox without choosing a mailbox database, then it will prompt you with the same error message. Choosing a mailbox database gets around this issue but as you pointed out the resource mailboxes there is not that option.
You will have to resolve this issue on your Exchange server. First, I would make sure the database you have isn’t excluded from provisioning by running a powershell command:
Get-MailboxDatabase <Databasename Here> | fl IsExcludedFromProvisioning,IsSuspendedFromProvisioning
Basically your Exchange is unable to find a valid database for whatever reason. Checking the event logs on the servers may help narrow down why Exchange is having this issue.
