Unable to add .asmx files as web references in Visual Studio 2010

When i try to add a web reference to my VS2010 project i encounter the following error.(the service is running fine , infact VS2010 detects it on its own when looking for services hosted on the system )

The document at the url http://localhost/_vti_bin/PPS/PPSAuthoringService.asmx 
was not recognized as a 开发者_StackOverflow社区known document type.
The error message from each known type may help you fix the problem:
- Report from 'XML Schema' is 'The document format is not recognized
 (the content type is 'text/html; char