Error Message Cs0433

HI All,

When I have run the web Application , It is showing the below specified Exception. so, It would be greatly appreciated if you can suggest me a solution for this exception.  

CS0433: The type 'Microsoft.Practices.EnterpriseLibrary.Data.Sql.SqlDatabase' exists in both Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET/.... and c:\Windows\assembly\GAC_MSIL\Microsoft.Practices.EnterpriseLibrary.Data\2.0.0.0__dd67af91bfe7d8d9\Microsoft.Practices.EnterpriseLibrary.Data.dll'

Thanks 

Shiva