Over Samba? There shouldn't be any problems; as long as the username & password are correct both connections should happen correctly.
Update: re: "Error 1219". This is a client-side error -- Windows only allows you to connect to a server as one user at a time. (See Microsoft documentation at KB938120.) This means the Windows machine has already connected as a different user, and so your attempts to connect again, as the correct user, are failing.
You need to disconnect the first connection before you can reconnect. Two ways I know of to do that:
Disconnect any reconnect-at-logon network drives from that server. Reboot. Reconnect to the server and make sure you give the proper username and password.
Use the net use /delete command from Windows' command shell (Start -> Run -> cmd; at the prompt type the command; you may need to specify a share name).
Update 2: If the users are already connecting to the server with one user, you won't be able to let them connect with a second user. You'll have to reconsider your share strategy, and reconfigure Samba to follow that strategy. (This isn't your fault; I blame Windows.)
Personally, I'd stick with individual users for each person, and consider using groups to control access to the shares. This works well if you have some shares that you want everyone to have read-write access to, and others that you want to be read-only for all but a select few users.
Update 3: The MS document linked above offers these two workarounds to enable connecting to the server as separate users. The general idea is, make Windows think it's connecting to a different server by using a different name.
Use the IP address of the server when you connect with the second username. (Use \\ServerName\sharename
when connecting as the first user, but use \\X.X.X.X\sharename
when connecting as the second user.)
Create one or more DNS alias(es) for the server to use when you connect with the second (, third, fourth...) username. (Use \\ServerName\sharename
when connecting as the first user, but use \\ServerAlias1\sharename
when connecting as the second user, \\ServerAlias2\sharename
when connecting as the third user, etc.)