The installation went well tried it but if you have the module else where on the page and you want it in the article also the module disappears from the normal position it is in and is only getting shown in the article.
Would be great if you could display the module two places at ones without having to make a copy of the module so that you have two identical modules.
Some modules are badly programmed so they can not be used on the same page twice (like the smartsearch module in the Joomla core). That has nothing to do with the workings of this plugin.
I installed it and got it up and running then i hit a wall. I can only make two objects. If i want to have more than two objects i have to pay.
Why then write that it can allow booking of one or more objects.
The payment doesnt work either.
So sorry that you aren't 100% happy with my module...
As you wrote I have tried to help you but as you could not provide the logs for your server it is impossible for me to try and solve your issue with why the Warning is posted.
If you reduce the logging level for Joomla from Maximum the Warning will not be visible and SFU will still work fine...
Please let me know if you can get hold of the logs.