Is the number you are entering start with 1160? Do not post the number, just answer if it starts with 1160.
A valid serial number is 24 number characters, No letters.
Hello "Just Shoot Me",
yes it begins with 1160 and has 24 number characters without any letter.
I personally haven't registered any Adobe software in a couple of years so I forget the process. But don't you have to select the software name and the version? Are you selecting LR 5?
Also Registration on the Adobe website is not required. All it does is list the software and serial number with your account. Which now with the CC subscription based products is MOOT.
If your LR 5 serial works correctly in the program to Activate it just keep hard and digital copies of the serial number for your own records.
You gain nothing by registering at the Adobe site.