Resolved issue today of IIS Server - PHP FastCGI 500 Error 0xfffffffe by deleting "Windows Temp" folder files. We used Cygwin to customize some permissions of "Windows Temp" folder and after few hours the website stopped working. The search online was giving all kinds of different solution except what I was looking for. I was hoping the stackoverflow will have answers but even this post didn't cover the issue I was running into. https://stackoverflow.com/questions/15302080/fastcgi-500-failure Restarting the IIS didn't work, but deleting temp files cleared the issue, but now the problem is how long before the site will go down again? Hope the issue is resolved for ever, if not; I will update this post later.