This is a little tip that took me sometime to figure it out:
This kind of issue happened when I was debugging a IntraWeb application created with Delphi XE3 in Windows 7. I often run Delphi XE3 as local administrator. I know, I know... but sometimes it is required for proper ISAPI debugging.
This application renders a control that supports drag and drop from Windows Explorer, when the browser also supports it (Firefox, Chorme, etc.). The issue then is: When you start the browser using ShellExecute (or CreateProcess for that matter), from Delphi XE3 (or any other version or software) running with administrator credentials, the browser is also running as administrator, right? But Windows Explorer IS NOT. So, drag and drop from Windows Explorer to Firefox, for instance, won't work. Applications running with elevated privileges and applications running as regular user just won't do drag and drop... Simple, yes?