Windows Share Not Visible in Explorer But Can Still Ping The Server

"Multiple connections to a server or shared resource by the same user, using more than one user name are not allowed. Disconnect all previous connections to the server or shared resource and try again"

This error is fairly common, and although it's pretty self descriptive, is usually misunderstood.

You can not connect to a share with more than one credential. If you map your S: drive to \\ServerA\c$\blah using the credentials joe.bloggs, you can not then connect to \\ServerA\c$\another_blah with a different set of credentials (say: jane.doe).

Check for any existing connections from machineA to machineB. To check this, on the machine acting as a share/server, right click My Computer, Manage, Shared Folders, Sessions. Is there a session already from MachineA to MachineB? What's the User? Is it different from the credentials you're trying to pass for this new session?

First make sure that the users have the install printer priviledge, although I guess you have already done that.

I think this might be a problem caused by drivers that arn't 100% standard. It may not work for you in this instance but one thing that has solved this error for me in the past is if you add the printer (and install the drivers) once as an admin user on each machine then the regular users, without admin rights, can then add the printer themselves.