This is my first post so i will try to contribute with a solution to a problem with TREX 7.10 (rev. 48) over windows 2008 R2
If you find the error on the httpserver with red light there is a simple solution
You need to do the follow change in the IIS
Then just add the <SID>adm user
Then restart the TREX
Also you need to be sure that you have set the Authentication method , ISAPI and CGI restrictions and in the Handler Mappings the ISAPI are enabled to the Server level.
As always follow the SAP install guides.
Hope this help you guys