ERROR: Object reference not set to an instance of an object

Problem occurs after the reinstallation of IIS in the web server (since out of a sudden --> might be due to a patch, the IIS is corrupted).

Accessing ASP page works fine in the localhost, but gives this error when accessing .Net page
"Object reference not set to an instance of an object".

Googled the web and found few links that teach on how to solve:

1. Support from Microsoft: http://support.microsoft.com/kb/810098

2. Common causes in VB.net: "http://codebetter.com/blogs/raymond.lewallen/archive/2005/06/23/65033.aspx"

3. Re-registering aspnet_regiis.exe -i: http://dev.communityserver.com/forums/p/474748/531732.aspx

Item #1 and #2 didn't fix my problem, but the #3 did.

Basically, to prevent this error, you need to install IIS before install .Net Framework. If you did the reverse way, the .Net framework somehow are not registered in IIS. Therefore, you need to run the command again "aspnet_regiis.exe -i" to install it.

Screenshot of running the command in cmd prompt: