Minimal prerequisites before continue
A: go sure you have setup IIS or Apache to run on port 81, if you can't do that then such cases are considered as uncooperative!
https://www.terminalserviceplus.com/docs/using-iis
https://www.terminalserviceplus.com/docs/using-apache
B: go sure you have configurated TSplus to run on port 80 and 443, or those that do not conflict, example port 88/448!
DO NOT SETUP TSPLUS AND IIS/APACHE ON SAME PORTS!
that means, if IIS was configurated to use port 81/443 etc., and TSplus was configurated to use port 81/443
THEN THEY WILL CONFLICT!
In such case go sure you followed the FAQ_IIS(or Apache), therefore reread the FAQ_IIS(or Apache) carefully and
fix these issues before continue!
C: go sure you access the server in browser by ports 80/443 (or any not conflicting) you have setup in TSplus!
that means if you have setup TSplus on port 80 but IIS on port 81, then you should access the link in browser
on port 80 like in example http://your_server, the HTTP requests will be forwarded from port 80 to 81 automatically!
To run TSplus with IIS or Apache as webserver you have to setup IIS/Apache so, that TSplus(html5service.exe) listens on port 80 and IIS(or Apache etc.) listens on port 81, since all HTTP1.0/1.1 requests will be automatically forwarded from port 80(html5service.exe) to port 81(IIS/Apache) to be processed by your third part webserver while at same time all HTML5-RDP requests will stay on port 80 and be handled by html5service.exe
Remember here, if you do not want TSplus(html5service.exe) to take port 80 so that IIS still remains on port 80, then you should be aware to setup TSplus on any other free port in bulit-in webserver mode as example on port 88 in AdminTool GUI => Web => Manage Web Servers. Be aware, just placing JavaScripts+html pages into root folder of your third part webserver like IIS/Apache doesn't make these webservers HTML5-RDP capable since IIS/Apache do not support HTML5-RDP on server side! But in such case if moved TSplus to non default port like 88 etc. the HTML5-RDP client will never work on port 80(http://your_server) but on that another free port as in given example http://your_server:88/
But if you by your any personal reasons can't accept that requirement, also move IIS/Apache from port 80 to 81, and do not want to start TSPlus on another free port than 80 then stop the setup since we can't help you out in such case, moreover support requests handling such uncooperative cases will be discarded caused by personal failure!
Error: "Third part webserver IIS / Apache failure, check FAQ!"
But if you agree with the requirements above and believe to have followed setup instructions in detail
https://www.terminalserviceplus.com/docs/using-iis
https://www.terminalserviceplus.com/docs/using-apache
you may still experience the error "Third part webserver IIS / Apache failure, check FAQ!"
In such case check if html5service.exe is really bound to port 80 and not an another service takes it already!
To check that run as Administrator "cmd.exe > netstat.exe -anb"
If an unknown running service is still displayed on port 80 instead of html5service.exe which represents TSplus HTML5 Java process then you have an another problematic case that is highly occurring when Microsoft SQL service was installed in addition to IIS. If that was your case and you have Microsoft SQL installed then check following steps!
1. Open - Start > Programs > SQL Server 2008 R2 > Configuration Tools > Reporting Services Configuration Manager
Sometimes it is not exactly named so as described above but should be called similar (as example SQL Server 2012 etc.)
2. Open - Web Service URL
3. Change port as example to 81
4. Open - Report Manager URL > Advanced
5. Click on entry with port 80 > Edit
6. Change the port to same as in step 3.
Be aware, problem with MS SQL server may be one potential case of many possible Microsoft services that may run on port 80. If you do not run MS SQL server but port 80 is still bound by unknown service then you will have to discover it on hard way which Microsoft service is still taking that port, also Google for it what could cause it! Sometimes the cause of busy port 80 is installed Skype on the server with enabled webservice, if so, disable or move it to another port, as example port 82 and/or 453for SSL accordingly! If no one of proposed solutions work then move TSplus away from these busy ports by setting up TSplus to listen on any non default free port in built-in webserver mode AdminTool GUI => Web => Manage Web Servers.