To enable error_log from IIS, it is not hard, but you have to consider the size of log might not easy to manage by Windows Operating System, unless you have installed the Resource tools kit to allow you to tail the log.
Alternatively, you may alway disable this feature but to enable when you needed.
Step to get it done.
1. Browse to the PHP directory that installed for PHP.(Usually go to C:\Program Files\PHP\, but this tutorial will teach you on simple directory of C:\php\)
2. Create a directory named log.
3. Edit php.ini by any text editor(notepad, wordpad, etc).
4. Change the following setting from php.ini
log_errors = on
error_log = “C:\php\log\error_log.txt”
5. Well done, you may check your PHP error_log from the error_log.txt as above.