On the last stages of the Kartris installer, you may see the following error:
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.
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.
[NullReferenceException: Object reference not set to an instance of an object.]
This error indicates that the ASPNET user and/or NETWORK SERVICE accounts on the machine do not have permissions for the web. You need to right click the web site folder in Windows Explorer, add the ASPNET and NETWORK SERVICE user account and give them FULL CONTROL permissions.
You should then restart the installation from the first step. Copying in the default web.config file is a useful way to ensure the install routine starts completely fresh.