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This is yet another twist to a fraud scheme that has been going around for years! First of all, there is no way you can be made liable for any amount of money for simply being named as a beneficiary! Especially if you never signed anything stating that you wanted to be a beneficiary, and that you accepted the liability.
The FBI has warned of similar frauds such as this. http://www.fbi.gov/scams-safety/fraud
If it were legitimate, a lawyer would have gladly advanced the "fee" in exchange for being retained to administer a large sum such as this! For the crook, the $20 is a small amount to pay in exchange for getting $11,500 from you! Take the $20, use it to buy lunch, and consider yourself lucky!
I wish I had a better answer for you! I personally have gotten many of these letters. I wish that it were real! It would solve many problems!
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Have a great weekend!