HI,
I came across your problem and just wanted to help out. Not knowing your setup and script I can just outline the probable caused
- Your script function simplexml_load_string($content) require an extension libxml to be present and enable to work which I believe your nginx server is not setup the same way as your apache?
Note: If you have written the script yourself, you may want to look at re-coding with another xml library for nginx if you dont want to fiddle with the server side.
I have put the lowest bid that freelancer allow me as I just want to help out your problem and build my feedback,