For US Sims 3 players, try this:
Go to Start
click Run and type in "regedit"
open HKEY_LOCAL_MACHINE\SOFTWARE\Sims\The Sims 3
double click SKU
Now change the value to a number between 1 and 7. Mines worked in 2
These numbers represent the region codes. Essentially you can change the region code for your Sims 3 game like this. I don't know which number applies to this WA EP so try each number one at a time until the install of WA works.