"The apps cannot be accepted by your Apple ID. These apps were already assigned to another Apple ID and they will be available in that Apple's ID's Purchases list."
Your second Mac probably came with the iLife Suite (iPhoto, iMovie, GarageBand) preinstalled. To be able to update them from the AppStore you need to "Accept" them with your current Apple ID after signing into the AppStore with the correct ID. You should see the iLife Suite in the "Accept" Portion of the Screen. After clicking "Accept" they will be moved to the "Purchased" section and you should be able to update them from the "Purchased" section, see the paragraph (Restoring iLife applications after Internet Restore of OS X Lion) here: http://support.apple.com/kb/HT4718
If you do not see the iLife Suite in the "Accept" section, then they already have been accepted using another Apple ID - check what Apple ID is set in your Users&Groups Preferences and update this if necessary:
See Re: Unable to update bundled ...
Good Luck
Regards
Léonie