A somewhat grumpy PC with error messages popping up all over the place and notes from MS saying that it was down to a problem with the anti-virus turned out to have a bad lump of memory - removing it cleared all the problems except one really irritating failure to read any external USB drive.
Looking at the list of drives I thought there were an awful lot of mapped drives but not my business to work out why this thing had to connect to so many other machines' drivers.
Anyway, I uninstalled all the USB devices and let the system put them back, which it did without any problems. But still no access to the workshops USB flash drive - which worked on other machines. It seemed to read it but the list of mapped drives just flickered.
Gawping at the list of mapped drives, I noticed that it had used every single letter including drive B. How really interesting I thought and turned it all off to go an post a question on this forum - just as well I stopped to make a cup of coffee on the way as it suddenly hit me - how can the system allocate a drive letter to the USB drive when there are none left? It can't so forget the coffee and back to the machine - disconnect drive Z: and reboot: stick the USB drive up it's orifice - and there it was all the time!
Moral - sometimes the blindingly obvious will stare you in the face for some time before you see it.

I don't know ~24 Mapped drives! To me that just sounds dumb
More like some tech wasn't sure how to map properly and just kept going until he used them all.

I've worked in huge enterprise before on large File Servers and no one maps that many drives, way too much. Hey this sounds like when they said 20Gig Harddrives were overkill Maybe we do need more letters.

Now off to map XY drive I go

Not quite - drives A, C and D were what I expected of them but rest all mapped to the same place. We will see what this is all about when I take the machine back to it;s home network tomorrow afternoon!