- Remote IIS server: run (as Admin because you need debug privs) msvsmon.exe (Prog Files\VS2010\Common7\IDE\RemoteDebugger\x64|x32)
- Make a note the Remote Debugger Monitor Server Name (usually looks like DOMAIN@USERID@SERVERNAME)
- Local Visual Studio: Debug > Attach Process > Qualifier = Remote Debugger Monitor Server Name
- Refresh and attach to the w3wp.exe process that closely matches your config type: x64, Managed, .NET 4 etc. You'll know you've got the correct process if your breakpoints are active (red dot vs. red circle and warning that breakpoint will not be hit).
Source: http://www.codeproject.com/Articles/38132/Remote-IIS-Debugging-Debug-your-ASP-NET-Applicatio