runtime error the type x exists in both x and y

i got this error in web site run under version 4 framework for user control assembly at runtime

Solution :

add this property to web.config file
<compilation debug="false" targetFramework="4.0" batch="false">

Explain for solution :
http://stackoverflow.com/questions/2596118/asp-net-error-the-type-foo-exists-in-both-temp1-dll-and-temp2-dll-pt-2

http://www.sellsbrothers.com/Posts/Details/1995