2 PCs Windows 7 (Ultimate) on a small business network (no Domain controller, and no Homegroup)With Password Protected Sharing turned off on PC 2 - when two users on different PCs (PC 1 and PC 2) have the same logon name (say John) and John (on PC 1) tries to access any Network shares on PC2 (which has PPS turned off), he is asked for a password (presumably because PC 2 already has a John and is confused) - since John on PC 1 does NOT have an account on PC2, he cannot access the shares - even though Password Protected Sharing is disabled.I thought that all USERS had unique security IDs, so why does this happen?

It is possible the SID's are also the same. I am assuming the machine names are both different. Try logging on using the machine name and then the user name. (separate with a back slash)machinename\John

Try turn on PPS. It should ask for a user account and password. Input the password on target computer to see the result.

Off course that WILL work, but that is not the point. Why should a password be requested when PPS is turned off... that is question.

Open GPEDIT.MSC (Group Policy Editor), go to Local Computer Policy --- Computer Configuration --- Windows Settings --- Security Settings --- Local Policies --- Security Options.Find Network access: Sharing and security model for local account.Change it to Guest Only.Turn off PPS should be the purpose to use Guest account to share files (like Simple File Sharing in Windows XP). Thus we should modify this group policy to apply.