Referenced-Assembly version auto updating

Question

Hi All,

I have on my machine (Windows 7, VS2010, .net 4.0) an asp.net 2.0 website which works perfectly.

When I try to publish this website on another server (Windows 2003 Server, .net 2.0) I get the message

Could not load file or assembly 'System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

So I checked with Reflector the App_Code.dll file. And indeed in the references there is System.Web.Extension 4.0. But if I go to the property page of my project the version number is 1.0.61025.

So I'd like to know what is changing this version number and how can I stop it ?

And also I'd like to know wtf ? I mean If I choose v2.0 it's for a reason and when I'll want to use the v4.0 I'll change it myself (Next step : It'll change my code because it thinks there is a bug) !

Thanks