Hi Antonio, I have a similar issue...
I have set up both Joomla 1.5 and Moodle 1.9.18 as per the instructions provided in the docs.
Moodle is installed ina directory under the joomla domain. e.g.
joomla.com/moodle
When running the health check everything passes ok, but then I get the "Received empty response from Moodle" error.
I have contacted my hosting company as you suggest above and they replied with:
As per your reported issue I check for your local system IP address into the server and the IP address is not blocked, It will be appreciated to assist you in better way if you can elaborate me with all the clear information & the exact steps you are following for getting the observation with error message.
I'm just wondering if that is a sufficient check? Do I need to ask them to do anything specifically?
Thanks,
Phil