I know this is a longshot but you must [in Disk mgmt.] assign it to a different letter than the one it has automatically, temporarily set i.e.
- if Disk mgmt. has automatically assigned E: then you cannot choose E: as a permanent assignment.
- if Disk mgmt. has automatically assigned E: and E: is what you want as a permanent assignment then you'll have to manipulate things to set it up- disconnect it,
- plug in others so that E: is used up,
- reconnect the desired one,
- disconnect the one using up E: and
- only then tell Disk mgmt. to permanently assign E: to it
The relevant tutorial is
Change and Assign Drive Letter - TenForumsTutorials
and the relevant Registry Key is
HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices
By the way, and this is another longshot, Windows can get itself confused about drive connections sometimes by remembering drives that have just been disconnected.I have never encountered this problem when assigning drive letters [only when using If Exist … in a script] but thought it worth mentioning.
If Disk mgmt. does not behave as expected then it is worth rebooting so you can start again with a clean sheet.
All the best,
Denis