Call to undefined function json_decode error

I Apologize in advance if this does not belong here but someone informed me this may be an Apache issue which i am not familiar with. I Noticed all the contact forms on one of my domains that I built in a form builder program are showing the error... Fatal error: Call to undefined function json_decode() in /home/storksnm/public_html/contact_form/fbapp/php/config.cls.php on line 351 This can be seen at - Removed - and other pages on that domain like - Removed - I tried re-saving the form in form builder and I even deleted all files on the server before uploading the newly exported forms and it still is happening. The weird thing is that I have a VPS and have numerous other forms made from the same program up and running on other websites on the same server and they are working just fine as can be seen here ... - Removdd - If need be, Line 351 of the error file reads: $this->config = json_decode( substr( $txt, strpos( $txt, "{" ) ) );