Try resetting the MWI indicator for that user's VM subscriber from Unity.
Path to follow: Search for the subscriber -> Select Messages -> Remove check mark for "User MWI indication" -> Save
Now put back that check mark -> Add MWI extension -> Save
Also check in your Exchange server, if there are multiple subscribers with the same extension (probably once the subscriber was deleted but was not deleted from exchange which will remain in the exchange and MWI could be picking up that subscriber)
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.