I wasn't able to get the Send to Excel functionality working when my QVW application was being served. I am using server version 9.0.7320.7. The problem was when the client was using Internet Explorer V 6.0 via AJAX.
I realized when the new window was popped out, the server name was being truncated. The old server name was 17 characters and the last two were being truncated off. I tried renaming the server (14 characters this time), unistalling Qlikview, deleting the C:\ProgramData\Qliktech folder and re-installing Qlikview but ended up getting the same error.
I was able to fix it by going into the registry and searching for the old servername and sure enough found it in a few places. The offending registry setting was
I realize now I could have gone into the registry and just changed this instead of the server rename and Qlikview re-install. I saw a few other references to the old server name as well.
I hope this helps someone since I originally struggled with it for a while.