AjaxControlToolkit.CalendarExtender and System.Web.Extentions version error

I have VS 2005, 2008 on my dev box.

New project from other developers who only have 2005 installed. When I build it I get error.

Error 1 Indirect reference is being made to assembly System.Web.Extensions version 3.5.0.0, which contains 'AjaxControlToolkit.CalendarExtender'. This Project references a prior version of System.Web.Extensions version 1.0.61025.0. To use 'AjaxControlToolkit.CalendarExtender', you must replace the reference to System.Web.Extensions with version 3.5.0.0 or higher.

When I change the version of Web.Extentions to 3.5 I get another failure

Could not load file or assembly 'AjaxControlToolkit, Version=1.0.20229.23876, Culture=neutral, PublicKeyToken=28f01b0e84b6d53e' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

Should I change the Public key for:

add assembly="System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"

to the newer one, or is this the wrong thing to do. the Server does NOT have 3.5 runtime.

TIA

If your server doesn't have the 3.5 runtime and you aren't able to install it, I suppose you must stick with the 1.0.61025.0 version of System.Web.Extensions.

I would guess that the problem you are encountering is because the AjaxControlToolkit dll that you are using was built with the 3.5 runtime. Thus, your project is referring both to the 1.0.6... version directly and to the 3.5 version through the AjaxControlToolkit reference, and getting confused. You might try downloading the toolkit source and building it from scratch, referencing the 1.0.61025.0 version of System.Web.Extensions. Then make sure to reference this toolkit instead of the default one.

http://ajaxcontroltoolkit.codeplex.com/Release/ProjectReleases.aspx?ReleaseId=11121

Also, you might try making sure that all the references to the System.Web.Extensions DLL version number are consistent, both in your project's references and in the web.config file. Note that if you have a reference selected, you can toggle the "SpecificVersion" property to True in the Properties panel; presumably this makes .NET more picky as to which DLL version it chooses.