As a skilled technical lead, I specialize in rectifying errors and resolving issues quickly and effectively. I have an extensive background in full-stack development, including proficiency in PHP, Java, HTML5, CSS3, and Javascript - just the skillset you need for these precise errors. Not only do I have the know-how to identify faults in website functionality or diagnose issues leading to pop-up error messages, but I also possess the invaluable troubleshooting techniques that you're specifically seeking.
Throughout my years of experience, I have gathered comprehensive expertise in debugging websites, even amidst tight timelines. One memorable project comes to mind when my quick thinking saved a client's website from a complete shutdown by identifying and promptly resolving similar issues within 24 hours. It's this extensive experience that enables me to work swiftly yet efficiently without missing any key detail.