I have finally got to the bottom of the problem...

Firstly - upgraded to Kix 4.21

The Homedrive mapping problem was solved by inserting some different code for Windows 9x users (This did not work before version upgrade).

The Group drives were not mapping because I had a Return statement buried in a gosub after an endif instead of before. This was despite checking it dozens of times.

Sorry for the red herrings!

Thanks