checkboxlist validation help

I found this article ( http://www.4guysfromrolla.com/webtech/tips/t040302-1.shtml )on how to create a customvalidator for the checkboxlist. Followed all the way thru, but when i load my page i get the following error, how can it exist in 2 places? How can i resolve this to use the validation on the page?
Compiler Error Message: CS0433: The type 'CustomValidators.RequiredFieldValidatorForCheckBoxLists' exists in both 'c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\294f506e\54827e67\assembly\dl3\0b4b5a36\08e15533_8dcfca01\RequiredFieldValidatorForCheckBoxLists.DLL' and 'c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\294f506e\54827e67\App_Code.5yh9snf-.dll'
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