I setup this machine some six years ago for a customer and at the time it had Vista Business and Office Professional 2007 pre-installed. They have decided it is time to upgrade the machine including moving to Windows 10.
I have upgraded the RAM to 16Gb and replaced the hard drives with a SSD and bigger SATA data drive, and have installed Windows 10 Pro onto the SSD. However when I have come to install Windows 7 Professional onto the drive the key is not accepted. The message (in Red) reads: "The key is incorrect. Verify that you have the correct key and then retype it.".
I know I have the correct key - I have a number of key finder programs (including AIDA64) which have never let me down in the past. I am using an ISO file from a standard Microsoft CD image which I have from my time as a TechNet member which I know works.
Can anyone tell me why I am getting this message and how I can resolve it easily.
NOTE: The customer couriered the machine to me before the Christmas holiday (they are 200 miles away) and I am hoping to return it when they get back in the office after new year (by courier).
TIA