This Error may occur in many cases like suphp+sssl or permission on file or folders but in my case this was on cPanel while accessing a test PHP page. Below was the complete error.
[Fri Feb 01 11:46:24 2013] [error] [client 22.214.171.124] SoftException in Application.cpp:422: Mismatch between target UID (99) and UID (509) of file “/home
/username/public_html/apps/test.php”, referer: https:/domain.com/apps/
[Fri Feb 01 11:46:24 2013] [error] [client 126.96.36.199] Premature end of script headers: test.php, referer: https://domain.com/apps/
Resoultion : The error was because our client configured the website on shared IP in cPanel and was accessing it using https://domain.com/ and as its Mandatory that SSL always needs a dedicated IP . Hence configuring SSL on shared IP for website on cPanel may give you this error.