Did it ever work?
Matt Laun explained that it related to the AMT database, which I think is the database of installed components of Adobe software. I believe his suggestion was to uninstall InDesign, run the CS5 Cleaner Tool, and then to re-install. Please try that.
Thank you for the help, however the cleanup tool didn't work for me, still came up with the exact same error #5.
I have also posted back to 'Midnight Paladin' to find out what steps he took to make his registration data accessible and to re-enter the old serial # as I believe I too may have the same issue as it is an upgrade license from v2 that I have. I'm hope I get this working soon....
The problem is now fixed. Apparently it was corrupted or otherwise inaccessible data in the registration database; I had to enter my old serial number (the one I upgraded from) again, but otherwise no ill effects.