Windows Networking (non server) refuses to accept verified password, even after reset

Windows networking refuses to accept password - even when copied and pasted after reset!

No server involved. Just one machine sharing a bunch of its files with two others. The share is set up and working for one of the other two.

Set up the local user account for the second machine, using the same password on the host as on the client. From the client, the password was refused. So once I confirmed that it was definitely identical at both ends, I changed the password to SIMPLE, sent a copy back to the client using a "Turbonote" and copied and pasted that into the password field. Even that was rejected.  Tried simple stuff like rebooting both ends but cannot get the "Server" to accept any password from the second client. And yes, it is clearly the password failing, not the connection. The turbonote helps prove you're on the same network but windows login is reasonably specific and distinguishes between failure to find a target and failure to authenticate. In this case, it clearly recognises the target, the share and the username. It's only the password it's refusing to accept and I haven't a clue how to bully it into submission.

Suggestions?