Trying to redefine a mapped network drive in place

I'm trying to redefine an existing mapped network drive using hte Net Use command line. I saw a question-answer for Win7 that suggested that I use:

Net Use [Drive] [New Mapping] - 

thus:

Net Use S: \\UNC path

However I get a 'System Error 85 - The Local Device Name is in Use' error

Any ideas what I might so instead, that doesn't need a registry edit?

You cannot create a network mapping if another mapping is established.

In order to create the new mapping, you first have to delete the old mapping.

You can do this by typing:

net use /d s:

Now that s: is no longer mapped, you can map it again.

net use s: \\hostname\share