User home folders on remote OD Replica – previously logging in, not any more.

I’ve recently been pre-building our new server and network-client config.

The difficulty I’m having now is that users at one of our remote sites who have a home directory on the OD Replica which is there who could previously logon can no longer do so: “You are unable to log in to user account “username” at this time. Logging in to the account failed because an error occurred”

The arrangement is this:
OD Master and fileserver at this location. Also contains user home folders.
OD Replica and fileserver at remote location, also contains user home folders (for users at that location).
Remote clients intended to work from that remote server have their home folders set in WGM to that server. The home folder was shared using the standard home folder creation method (Svr Mgr, File Sharing, Share Points, enable automount and home folder protocol options).

Permissions were set on the Users folder to allow network users and admins to create folders (specifically: root – R&W, admin gp – R&W, others – none)
Actual network user folder permissions are: owner (username) – R&W, staff – Read only, everyone – read only.

In order to test the new accounts and remote home folders were working, I logged the remote network users on locally (still using their remote home folders). All logged on fine, though fairly slowly as you would expect (accessing home folders over the WAN).

Came in the next day to finish creating and testing users, and none of the newly created (that day) users could log on with their home folders on the remote site. Nor could any that were working the previous day.
Any local users (with home folders on the local server) could log on fine, and any remote users could log on fine once I switched their home folders back on to the local server.
Kept getting that irritating, undescriptive “an error occurred” (full error in at top of page).

Users that cannot log on can access AFP shares on the local server and on the remote server – however they cannot access the /Users/theirusername share (on the remote serer) – which says an awful lot about why they cannot log on. However I can’t work out why they shouldn’t be able to access their own home folders on the remote site.

As far as I know, no network config has been changed, nor has the WGM or Svr Mgr setup been altered.
Where the **** do I start? Logs to look at? Things to try?