I have the serial number but it begins with an "EMW..." rather than a numeral. Adobe Help said for me to ask the real experts here in the forums. They couldn't figure it out.
I'm pretty sure for the v5.5 I did an online upgrade years ago, and so the newest physical discs I have are for AE7. FYI - I'm doing this to use an old Neat Video plugin that I don't want to upgrade...
Oddly, it worked a few days ago. I have no idea what has been changed. The original version of this software lives on my old MacPro. I'm on a new 5K iMac. I'm currently running CC2015.
-- A Proud member of the Reality Based Community since 1992.