The web server returns a response which does not declare the content type of the web page.
httpd.log debug will show a result similar to:
[ 16273][8 Feb 14:40:08][APACHE] [CVPN_INFO] Cvpn::WebHandler::analyzeContentTypeByContentBeginning: called for URL (http://someserver.somedomain.com/SomePage.ashx)
[ 16273][8 Feb 14:40:08][CONTENT_ANALYZER] [CVPN_INFO] Cvpn::ContentAnalyzer::analyze: called with (1136) bytes
[ 16273][8 Feb 14:40:08][CONTENT_ANALYZER] [CVPN_DUMP] Cvpn::ContentAnalyzer::findfirstAsciiChar: visible char at 0
[ 16273][8 Feb 14:40:08][CONTENT_ANALYZER] [CVPN_INFO] Cvpn::ContentAnalyzer::analyze: UNKNOWN