I have found that it is possible to have several computers using the same username to connect to a samba share. However, I do keep getting this error in the syslog:

where 590 is the PID of the computer accessing the samba share...

Could this be causing it? Any possible ideas?

Does this share belong to the username being used to access it, or is a share open to all users?

There is nothing remarkable about multiple connections to a share with the same username. There may, however, be a limit somewhere on the number of concurrent connections. What kind of Samba security is in play here? I.e., what kind of Windows OS is doing the authentication?

Yes, the share is owned by the username that is accessing it.

The stations are running Windows XP. It is a rather simple setup with no Domain Controller. The shares are just mapped on the station with the username/password combo of the owner of the shared files.

Everything is accessible, but everytime sometime is accessed this error shows in the logs. I initially thought that maybe even though I mapped the shares with the correct username and password that maybe Windows was being weird and initially sending the local username/password to access it but then when that was denied it used the one specified in the mapping... Thus, I created a users.map file for samba and mapped any possible local users to the correct Unix/Samba user and added the entry to the smb.conf file.