Is this from any workstation or just one?
The fact that you can no longer map via the host name means the server or workstation might have lost contact with your Active Directory's DNS server.
To test this, go to C:\Windows\System32\drivers\etc on a workstation and add a line to lmhosts (If there is just a lmhosts.sam then either rename it without the .sam or create a new file named "lmhosts)
add to it a line with the ip address and server name of your SL installation in the form of
xxx.xxx.xxx.xxx Servername
and see if you can map a drive in the proper \\servername\share form.
See if this then solves the rest of the issues.
if it does, then you need to figure out what is not connecting to the DNS server.