SUBST: How to map to D: drive

Question

subst x: myFolder

Works as expected. Maps a new drive 'X' to the files of "myFolder".

subst d: myFolder
Invalid argument - D:

Why is that?

Does this mean, that it is not possible to map do D:\ ?

subst (without parameters) prints nothing (or only X: if mapped). So D is not subst already.

Any clues about that?

Answer 1

Oh dear lord, I feel extremely stupid now.

The Laptop I am working on has mapped the DVD drive (which is deactivated but still mapped, hence you can not see it in the explorer) to D:\