You try and update publishing for a content type in your SharePoint 2010 content type hub.  You receive an error message that "No valid proxy can be found to do this operation".  This means that either you don't have your content type hub URL properly specified in the managed metadata service application in SharePoint Central Administration or the URL that you are using an AAM of the web application and your MMD proxy is configured on an internal name (example http://sharepoint instead of http://sharepoint.net).  You need to change the URL of the proxy by using powershell (you can't do it from the MMD service app once created).  If you want to get past the error you can also switch context (ie use http://sharepoint/hub) instead of http://sharepoint.net/hub.  Good luck