Hi - related to problems in R2: Check IIS on Windows 2008 R2 systems.
Open Inetmgr and open the IVR websites.
Check one simple thing - Do you see MIME TYPES THERE? If you do not, then uninstall 3CX. remove IIS role.
Restart
Then add IIS role again and leave everything default.
Install 3CX and you should be ok.
Another good point mentioned is the 3CX Application pool.
On windows R2, adding the IIS role created some hassle for us as well (It was officially released last week right?). This is why we said that it was not 100% ready. We encountered various errors too.
There is a good article on the wiki named troubleshooting Error in the IVR.
http://wiki.3cx.com/documentation/troubleshooting/troubleshooting-ivr-errors
In R2, we found that removing the role and adding it again gets everything working.