Where does IIS 7.5 log errors?

To report errors in Event Viewer, go to your php.ini file and make sure logging is on.

log_errors = On

Then enable error_log to write to syslog (with is Event Viewer on a Windows machines)

error_log = syslog

On my IIS 7.5 server I found this code in the php.ini file right down the bottom.

[WebPIChanges]
error_log=C:\Windows\temp\php54_errors.log
upload_tmp_dir=C:\Windows\temp
session.save_path=C:\Windows\temp
cgi.force_redirect=0
cgi.fix_pathinfo=1
fastcgi.impersonate=1
fastcgi.logging=0
max_execution_time=300
date.timezone=Australia/Canberra
extension_dir="C:\Program Files (x86)\PHP\v5.4\ext\"

I'm not sure if all of the above code is required because I'm not great with php.ini files but I can confirm the error log file is reachable and working.

This fix still requires the following if anyone is wondering.

log_errors = on
error_log = syslog

For PHP v5.3, look here:

C:\Windows\Temp\PHP53_errors.log