screensharingd is not accepting username/password

Hi,

We have a mac mini that does not accept my credentials via Screen Sharing. I've enabled Remote Login & Remote Management and set the VNC password ('VNC viewers may control screen with password') to the same as my username 'geertl'.

When I try to connect from another mac mini or a Ubuntu system (with Remmina client) I always get following error (system.log):

Jun 7 18:01:01 mac screensharingd[2277]: Authentication: FAILED :: User Name: geertl :: Viewer Address: x.x.x.x :: Type: DH

VNC access is just fine (with e.g. TightVNC viewer) :

Jun 7 18:01:36 mac screensharingd[2282]: Authentication: SUCCEEDED :: User Name: N/A :: Viewer Address: x.x.x.x :: Type: VNC DES

In this VNC window I can then enter my password and login without problem. Also SSH works without problem from a Linux box:

~# ssh mac -l geertl sw_vers -productVersion

Password:

10.11.5

It's just the screensharing that is not accepting my password and/or username. Mac has been rebooted, screensharing reconfigured both via GUI as via CLI, 'Account Name' and 'Real Name' were aligned and put different none of them work. Firewall is disabled.

We have another mac which is configured identically (same username, same network, ...) where the Screen Sharing works fine.

Any pointer highly appreciated!