Calibre Portable and Assigned Letter to Portable Drive issue

I use Calibre Portable and have never had any issues until I assigned a static letter to the portable drive.

I assigned it "G" and recently the drive lost the assigned letter G. I tried to reassign it and it is no longer in the listing so I re-labelled it drive N.

Now whenever I boot up Calibre Portable - and I am trying to open a book or move between libraries - I received a message pop up:

Calibre-parallel.exe - No Disk

There is no disk in the drive. Please insert a disk into drive G.
Any assistance or suggestion s would be greatly appreciated.

:help: