My websites are hosted on different VPS in different companies and different WHMs. One strange thing is happening that one of my custom websites is working on VPS1 and WHM/cPanel but isn't running on VPS2 and WHM/cPanel. I think it's happening because there is difference in configurations of different companies or PHP/MySQL isn't compatible witn the custom website on VPS2. What should I check in WHM or suggestions to fix the problem?