Back link error A link to http://www,,, could not be found at the specified URL

I am getting problem with PHP code although I checked and test the code is fine.

I have link partner page in PHP and its connected to database for back links. When I placed the reciprocal link into other website and insert the link into Reciprocal field. The target website did not found the back link in my link-partner page.

But the target website reciprocal link checker working fine with html file on my website.

My question Why auto link checker works with HTML file but do not work with PHP ? and how can I resolve it ?