Missing gallery in Local Government Maps and Apps, HTTP 500 error "Unable to decrypt token"

Error Message

Local Government Maps and Apps gallery only shows the messages "Loading Maps and Apps..." or "No items were found" after March 21, 2012.

Viewed in a web browser debugger, the response to the following URL

http://<server>/MapsAndApps/proxy.ashx?http://www.arcgis.com/sharing/search

Code:
{"error":{"code":500,"message":"Unable to decrypt token: ...

Note:
This error applies to the Local Government Maps and Apps Gallery download.

Cause

Local Government Maps and Apps connects to content stored in a group on ArcGIS.com, so the site is configured with an ArcGIS.com authentication token for access rights. The encryption that ArcGIS.com uses for tokens was improved on the night of March 21, 2012, and this improvement requires the Maps and Apps site administrator to regenerate the site's access token to use the new security.

Solution or Workaround

1. Generate a new token using Token Helper. The page
   displays the token and the UNIX-style expiration date (milliseconds since Jan. 1, 1970).
2. Copy the value in the pair of quotation marks after the keyword 'token'.
3. Paste that value into the site's configuration\config.txt file inside the pair of quotation marks that follows the keyword 'galleryOwnerAccessToken'.