I also have the same problem having upgraded an hour ago.
now it won't run.
Might be worth elaborating: what happens, exactly, when you try to run it.
Sorry to crash into ozprintshop's original question but when I click on the icon LR5.6, nothing. I try as administrator, nothing and in the program panel I also try to open , still nothing. No error codes, just nothing happens.
Assuming windows 7 also (eh?), have you looked at the process list after double-clicking the "icon", to see whether the lightroom process ever starts (or is already started..)?
Consider also checking the system event logs, to see if a system error was logged.
No evidence that LR starts and I cannot spot a system error
Could you give the Event Viewer a look?
If you open it and look into System
%windir%\system32\eventvwr.msc /s (you can type it in in the run input field on the start menu)
Look into Windows logs/Applications
Check if you see any errors - when you click on them you can see the name of the application and some error info.
Hopefully you'll see something there that might help.
Thanks for ideas re event viewer which I will look into. However, I have now got LR5.6 to work (and read my Nikon D810 Raw files) by uninstalling the download I made via my CC Apps panel and then downloading afresh direct from Adobe Lightroom downloads page. I have no idea why this should work but at least I am up and running. Hope this helps any others in same situation. (I did try to do a "repair" but this made no difference on the original download)
I had the same problem, and I also believe it is caused by having the Creative Cloud application doing the updating of LR. I "fixed" the problem by:
1. Uninstall Lightroom
2. Download the stand-alone LR 5.6 installer from here: Product updates
3. Install LR 5.6 using the stand-alone installer, instead of using the Creative Cloud application.
Worked for me.
All back to normal !
Installing the standalone version just postpones the problem until you install the cloud version, again.
The SLCache folder has bad data in it that confused LR 5.5 and again LR 5.6 until it was cleared, via Solution 4 on this page. Of course there could be other issues, so trying each of the solutions in order could be useful, but Solution 4 is the one that finally worked for me, with LR 5.5 on my home computer, and LR 5.6 on my work computer, where I'd installed the standalone 5.5 to bypass the issue and it came back with LR 5.6:
Once you remove the contents of the SLCache folder other Adobe programs will ask to be relicensed like Elements via a serial number or the cloud programs by logging in, but that is just once after you clear it not each time.