Usman Asar

Good to know it worked, else I had always left UrlRewrite portion in setting up Moodle on IIS 7.5 onwards and all sites worked fine so far. havent even thought about LDAP server being culprit But, another thing added to my knowledge in troubleshooting if LDAP servers are separate from Moodle.

You dont have to setup URL ReWrite, as sometimes slash aurguments does not work properly with URL ReWrite (admins tend to disable slash arguments in Moodle if URL ReWrite is present) , but make sure your cgi.path is enabled (like I mentioned above), also your PHP is properly setup (as you as well have to give permissions to a temp/sessions folder in PHP), if in doubt, i'll link you to a video tutorial that will guide you setting up IIS for Moodle properly.

Elaine,

Though all my installation on IIS with either of MySQL or MariaDB are working fine without needing the URL re-write, but because it is mentioned in setting up Moodle on IIS, so may have effect as SQL-Server tend to behave little differently, you can read about setting up URL ReWrite here https://docs.moodle.org/30/en/Internet_Information_Services#URL_rewriting

In addition,  how have you setup Moodle on IIS? as for PHP IIS requires slightly different settings in PHP than on Apache, is your cgi.fix_pathinfo is enabled in PHP settings?

Elaine,

though MAY not have to do with URL Rewrite, but have you enabled ReWrite for moodle in IIS?

in addition, in Moodle, go to Site Administration > Users > Authentication > Manage Authentication and make sure LDAP plug-in is not disabled (means EYE opened), this is in addition to LDAP plug-in.

Do check LDAP plug-in as enabled first, then do the URL re-write configuration.

Websites aren't dependent upon just one factor to perform, starting from hardware to network, all things play equal role in performing website. Where you haven't even mentioned which server you're using? any PHP accelerators? what hosting?.