Quite simply, if Windows cannot properly load your Org.eclipse.atf.mozilla.swt.browser_0.2.1.v200703161053.jar file, or your JAR file is infected with a virus or malware, you will encounter an error message. Please see "Causes of Org.eclipse.atf.mozilla.swt.browser_0.2.1.v200703161053.jar Errors" below for more information. When Do JAR Errors Occur?