Data Service and Linq DLL reverts to a different version after building

We are currently using an ASP.NET project that uses Data Services and Linq. Before when the project was newly created via Wizard/Template. The generated DLL in the bin folder has the version 3.0.40818.0 but each time I rebuild the versions of the DLL reverts back into version 2.0.31005.0. I tried checking the referenced assembly and it says

System.Data.Services.Client is version 3.5.0.0 while the runtime is v2.0.50727 (I believe the runtime version is not related to the version of the DLL).

Also for the assembly of the System.Xml.Linq has version 3.5.0.0 in it. I also checked the global assem开发者_开发问答bly cache and it only has version 3.5.0.0 in it.

Does anybody know why the version is changing?