This might sound silly - take the serial number and copy it into Notepad. This will strip off the formatting, and then copy it again, but this time from what you pasted into Notepad.
Then launch the install again and paste it in, using the Notepad-copied serial number.
I have seen weirdness in the past where the above has worked - (might have been for registration code, brain is fuzzy, but it did work so give it a shot).
It instead it is the registration code, do the above for that. Please note that his may not be what is wrong, so it might not work, but is worth a shot.
Bob Bone