Resolution:
One of the Possible reason could be :

Make sure your Process's Start and End activity is using XML Element Reference and the element you are referring to has to have a unique name space. If you have not specified any target namespace for that schema, webservice Wizard will not let you generate the webservice for that process. Choose the XML Schema of that element and provide a target name space to have this working.

Keywords:WEBSERVICE,GENERATE,PROCESS,GRAYED,DISABLED ,TargetNamespace