Hi,
Yes it presents the screen and immediately whitens and freezes.
It is happening to all users, on all machines and using all browsers.
No cache extras are installed, though 2.6 has a note about it in the Notifications. Is this essential? Should I try this first?
On my Test Server I reinstalled the backup from before the Upgrade and everything works fine but, as mentioned, I don't want to be locked into a version which cannot be upgraded. It is clear that something has happened during the Upgrade, but no idea what! It happened to both Servers but as it was not apparent I thought that it was successful on the Test Server and then upgraded the Production Server!
Error Logs do not appear to show anything out of the ordinary.
I am about to apply your suggested steps and will report back.
Peter