Apologies for the delay in replying.
This appears to be an obscure bug in the USB software whuch affects a small proportion of units. The message is "UNPLUG USB", made meaningless by the missing B.
It can be fixed by updating the USB software, but we are not keen on having our users do this as any problems can either trash the H9 or damager the computer used to do the download.
For this reason we would like you to send your unit to us for a no cost repair. Please contact support@eventide.com mentioning this post.