You're going to take me to the Grave

Before we get down and dirty, open up Notepad in administration by right clicking on Notepad and selecting Administration. If you miss this step you will get a "Access denied" later on. 

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Now that that is done, in Notepad select Open and navigate here to C:\Program Files (x86)\Electronic Arts\The Sims 3\Game\Bin and find the default.ini. It is a configuration file. 

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Next scroll till you find [Version], it should be at the bottom and take note of the CompatVersion and WorldBuilderCompatibilityVersion as these are important for the next step. Make sure you know which is which.

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Now select File and open again, this time navigating to C:\Program Files (x86)\Electronic Arts\The Sims 3 Create a World Tool, from here select Default.ini or just Default. Again this file is a configuration file. 

Open this file and navigate to the [Version] section.

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Now with the CompatVersion and WorldBuilderCompatibilityVersion numbers you collected in the base game Default.ini, match them in the Create a World Default.ini. (Note:Mine are both the same as I have already done this.)

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After you have changed those variables go to File save, DO NOT CHANGE THE FILE NAME. Close Notepad and Try opening Create a World Now.