BizTalk Application build Error - Duplicate System.Web.Services DLL

Hello

I am getting the error after migrating the source code from BizTalk 2006 to BizTlk 2010. The error details is as

An assembly with the same identity 'System.Web.Services, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' has already been imported. Try removing one of the duplicate references.           c:\Windows\Microsoft.NET\Framework\v2.0.50727\System.Web.Services.dll               

IS this error because of two versions of Dll (System.Web.Services.dll ) available in the system.

Please suggest the solution.

Regards,

Manish