使用PHP上载图像时出现500内部服务器错误

I'm offering users the ability to upload files using an online form, but I keep on getting 500 internal server errors whenever the file upload is processed. This is what I know:

• The problem isn't related to php.ini. I've checked the max file upload size, and it's set at 2 megabytes. I get the same 500 internal server error uploading 3kb large files, as well as 100kb large files.
• The problem isn't related to file permissions. The php file I'm using to upload, upload.php, has permissions set to 664, and the upload folder, called upload_pic, has folder permissions of 755.
• This is not an issue with the code. The exact same code was working on my previous server. I recently bought a new server and am migrating the sites over, and this is where I'm getting my problem.

I've looked online for the past two days, but I just can't find what's causing the problem. I've seen many issues similar to mine, but most of these were resolved by changing file/directory permissions, or making edits to php.ini.

Does anyone have any other proposed solutions?

Thanks!