Help (php issue)

Hello, i'm a web developer using PHP under Linux and Nginx working on a medium project, using composer and many open source php libraries, the site was working so good untill and eventually got an error : *Warning*: require_once(/home/....): failed to open stream: Too many open files in */home/.....* on line *25* we couldn't solve this or even figure it out, we searched the web and php community but there was no results, we heard it's a bug in PHP, we're using PHP 5.5.3, can you let us know please how to solve this ?! Thanks in advance, kind regard.