Description:
------------
is_file and file_exists() bugged?

Reproduce code:
---------------
I am kind of a newbie at coding PHP, but I recently inserted the code 

//if(is_file("$main_link_files/$file"))
if(file_exists("http://www.rfiles.com/rp/downloads/files/remo_test.zip"))
	{
		header("Location: $main_link_files/$file");

	}
	else
	{
		include('inc/site_header.inc');
		echo "Sorry, the file you have requested is either invalid or missing.<br> Please try again later or contact an administrator.<br>$main_link_files/$file";
	}

and all I end up being returned is false, leading me to the "Sorry, etc". I've tried, is_file() and file_exists(), and have ended up with the same result.

Now, I'm not sure if this is a problem, but I am actually hosting the file off of my webspace, which is on another webserver, apart from the script, which is hosted on my server machine.

I troubleshooted this for hours, and still come up with false, but yet the direct link works from the header if I remove the checks.

I even made sure all the permissions are set to 777 in the CHMod file properties.

Any help would be very appreciated.
Thank You.

Expected result:
----------------
True.

Actual result:
--------------
False.