My environment is SharePoint 2010. I was working on some master page changes and accidently I opened default master from (C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\GLOBAL\default.master) in SharePoint designer for some reason it removes the "~/" from the path of following user controls
<%@ Register TagPrefix="wssuc" TagName="Welcome" src="~/_controltemplates/Welcome.ascx" %> <%@ Register TagPrefix="wssuc" TagName="MUISelector" src="~/_controltemplates/MUISelector.ascx" %> <%@ Register TagPrefix="wssuc" TagName="DesignModeConsole" src="~/_controltemplates/DesignModeConsole.ascx" %>.
I opened my default master in notepad and corrected the path by adding the tilde and slash but still my master page is not loading properly and i get the "File Not Found error". In view source the error is "/_catalogs/masterpage/_controltemplates/Welcome.ascx does not exist"
Best Regards Vivek