Change the Debugger Port
The HTML5 Builder debugger needs a port to work. By default, it uses 9001 TCP port. Chances are another application of yours might also need that port, hence blocking it. In that case, the debugger will not be able to start. You can then change the port used by the debugger to avoid this issue.
- Open HTML5 Builder.
- Go to Home > Options > PHP > Internal Webserver.
- Change Debugger Port to a different value. For example, you can use 33333 port. In any case, try to avoid ports used by other applications installed in your system. Click OK to apply changes.