Sitecore Admin Tools (e.g. cache.aspx) not working

Recently I was tasked to figure out why tools under /sitecore/admin folder are not working. Tools such as cache clearing (cache.aspx).

Now the system is Sitecore Intranet Portal setup running on Sitecore 6.1 with multiple integration points such as Active Directory and Sharepoint. Naturally the configurations are quite many. Anyway when I am trying to access the tool it will throw an arrow as such

Server Error in '/' Application.

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Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[NullReferenceException: Object reference not set to an instance  of an object.] Sitecore.Nexus.Web.HttpModule. (Object sender, EventArgs e) +340 System.Web.SyncEventExecutionStep.System.Web.HttpApplication .IExecutionStep.Execute() +79 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean&  completedSynchronously) +170

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Version Information: Microsoft .NET Framework Version:2.0.50727.5420; ASP.NET Version:2.0.50727.5420 

Figuring out the issue, the error was caused when

<location> tag is added.

Removing it solved the problem