Screen sharing stopped working after 10.10.2 update

[korun]

Screen sharing between my iMac and Mac Mini stopped working after I applied the 10.10.2 update. I'm trying to access the Mac Mini from the iMac. I get the standard error message advising that I should check the Mac Mini is on the network etc. etc.

File sharing works well. I can copy files between the two Macs and can move and delete files on the Mac Mini. I always access Screen Sharing using the same user credentials as for File Sharing.

I have tried:

• Turned Screen Sharing off then on again on the Mac Mini.
• Checked the IP address many times.
• Invoked Screen Sharing using the application (in CoreServices), the Connect to Server dialog (command-k) and the Network dialog (command-shift-k).
• My Mac Mini does appear under “Sharing” in the sidebar suggesting (with the working file sharing) that this is not a networking issue.
• Reinstalled 10.10.2 using the combo updater.
• Adding port 5900 to the vac command (i.e. vnc://nnn.nnn.n.nnn:5900).
• Deleted the screen sharing prefs files (on the iMac).
• Deleted relevant entries in my KeyChain (in the hope SS would pop a login dialog - but it didn’t).
• Made sure the Mac Mini is awake.
• Checked logs but can find nothing at all on Screen Sharing.
• Installed the ARD update on both machines.
• Checked Firewall settings - Screen sharing is specifically allowed (and there are no other sharing functions blocked).

Nothing has worked.

The iMac is connected to the router by cable; the Mac Mini is connected by wifi.

Screen sharing worked under 10.10 and 10.10.1. Now it doesn't. I haven't played with settings except as stated above.

Does anyone have any ideas ? This has me totally stumped.