Alison,
It is an access issue. The Addin's were installed under your profile, so the config file is located under a path similar to the two lines below.
C:\Users\%UserName%\AppData\Roaming\ArcGIS4LocalGovernment\ConfigFiles
C:\Documents and Settings\%UserName%\Application Data\ArcGIS4LocalGovernment\ConfigFiles
When the other user logs on they cannot access your profile information. So, by default the addin will create a new loaded.config for the user that is logged in( the new config is the default our the box version). I am assuming you have a loaded.config file for your own data, if yes, then you will have to copy that version of the loaded.config to a location the other user will have access to it, then have the user load that loaded.config under their profile.
Cheers,
Lindsay