GPS or Geo tagging is not a primary focus of Tag That Photo.   We use an open-source cloud service to do location searches and conversion to GPS coordinates called OpenStreetMap.org.  Sometimes you may see messages like "Internet connection not available" if TTP cannot connect to their servers.  This could be caused by firewalls or other software filters.  And, also, if you submit too many requests in a short period of time they limit the number of "hits" on their servers.

If you want a really good tool for GPS tagging that is dedicated to that task please try GeoSetter.

You get enhanced features and the ability to batch tag a set of images with location data.

Here is a good Youtube tutorial on using the product: