you probably used a corrupt subject to snap to, you can not know that, but it happens more.
Just ignore the error, go on with what you were doing, mapping, tagging, titling. When you´re done, just close the upload tab and go to your Panoramio page. The uploads and changes are live, the button at the bottom doesn´t have any other function as bringing you to your photo page.
Everything will be there, except that "snap" on photo(s) affected. The same will happen if you will try to snap to that corrupt subject afterward. Look for an other subject or ignore.