Thx for the reply. The issue has been resolved.
I swapped the problem HDD with a spare one I have. I'll install the problem HDD in a PC and reconfigure the partitions with fatXplorer there.
A related question:
Why is it that the XBpartitioner standard preconfigured size for partition 2 is set at 500MB? Both Apps, Emu's, ROMS and Games folders are automatically set up there when running the full setup from i.e. the (CERBIOS) Installer Disk, and will run out of space in no-time, making it necessary to at least move the "Games" and "ROMS" folders to one of the bigger partitions.