Please make sure your site's 'linkmachine' directory and 'url.dat' file have all write permissions turned on.

LinkMachine is unable to write to a data file named 'url.dat' within your site's "linkmachine" directory.

See this page for a list of which files and directories need to have their write permissions turned on in order for LinkMachine to work correctly. See this page for information about changing the write permissions of a file or directory.