Blank pages due to file/path not found

Hello,

I have had several WordPress sites running for a while now with no issues. I was using IIS 6 + PHP 5.3.10 until tonight, when I decided to update PHP to 5.3.27 and install/use FastCGI.

Now, all of my WordPress sites are fine, except for one! I am getting the following error message:

[29-Oct-2013 03:33:17 America/Vancouver] PHP Warning: require(./wp-blog-header.php): failed to open stream: No such file or directory in E:\home\www\redlounge.ca\index.php on line 17
[29-Oct-2013 03:33:17 America/Vancouver] PHP Fatal error: require(): Failed opening required ‘./wp-blog-header.php’ (include_path=’.;C:\php\pear’) in E:\home\www\redlounge.ca\index.php on line 17

I have spent the last few hours reading other people’s posts on here and other forums, and it seems like it is a path issue. If I open index.php and go to:

require(‘./wp-blog-header.php’);

and replace it with

require(‘wp-blog-header.php’);

everything works fine! But the issue is that I need to do this (remove the “./”) from every single .php file in my WordPress directory to get everything to work, and I don’t want to do that at this point (I would rather figure out what the real problem is).

This is quite puzzling, as I have working WordPress sites on the SAME IIS server, with the SAME WordPress version and I did not have to change ANYTHING.

Yes, I could try reinstalling WordPress (or change all the files manually to correct the path), but at this point, I am DYING to find out the exact cause of this, as I am sure there is something I need to rest on the IIS instance for this site to make it work (I don’t think I need to change anything on the PHP or WordPress configs, as all the other sites are working with the same config, so the only thing I can point to is some setting in IIS for this web instance).

I would really appreciate it if someone could help me figure this out and learn a thing or two along the way.

Cheers,

-f.