两个包含来自同一文件夹。 一个工作,一个不工作 - PHP

I'm trying to do some includes in my PHP file. Both the files I'm trying to include do off course exist.

This one works:

include("/folder/subfolder/firstfile.php");

This one doesn't:

include("/folder/secondfile.php");

How is this possible, since both includes are coming from the same folder.....?

The errors I'm getting

Warning: include(/folder/secondfile.php) [function.include]: failed to open stream: No such file or directory in index.php on line 2

Warning: include() [function.include]: Failed opening '/folder/secondfile.php' for inclusion (include_path='.:/usr/local/lib/php') in index.php on line 2

File structure

Root has folder in it. The includes are made from a file that is in another folder in the root.

PHP extension is missing in the second include().

include("/folder/secondfile");

Change to

include("/folder/secondfile.php");

Also make sure that it is in folder folder. If it is in subfolder, don't forget to include it to path like :

include("/folder/subfolder/secondfile.php");