I developed a website, using php/mysql running at IIS Server as CGI Server API.

Suddenly it gives me error 500 after two weeks. It has lot of scripts but index.php home is working. But other script that has header redirection

What's wrong with my scripts.

livehttp addon of firefox says..

GET /allplans.php?lang=ar&cat=1 HTTP/1.1
Host: www.myhost.com... [edited]
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:14.0) Gecko/20100101 Firefox/14.0.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
Cache-Control: max-age=0

HTTP/1.1 500 Internal Server Error
Content-Type: text/html
Server: Microsoft-IIS/7.5
X-Powered-By: ASP.NET
Date: Mon, 03 Sep 2012 08:09:13 GMT
Content-Length: 1208
Connection: Keep-Alive