VS 2010 - Third Party Assembly References

[C#Jonathan]

Hi, I've just migrated an application to Visual Studio 2010 and upgraded a third party add-on called Visual WebGUI to .Net 4. I now have a problem with assembly references to the third party DLLs
The latest version of the Visual.WebGui.Forms DLL for example is at 4.0..... .
Our application is looking for the previous version. The software builds fine and executes.
An unhandled exception was generated during execution : Could not load assembly or reference Visual.WebGUI.Forms 3.0.5701.0............... . The version 3.0.57010.0 is the old version of the DLL.

Could anyone please tell me what I've missed during the migration ?
There are four projects in the solution. I have targeted each of them to .Net 4.0 using the Properties Window. I've searched the "Entire Solution" for string refernces to the Version number 3.0.5701.0 and updated the relevant ones to 4.0.5701.0 which is the right reference.
The files changed include the Web.config file and various .csproj files and no others as far as I can recall.

I have run the search again and can't find any more instances of the old reference.

So how does the project still refer to the old DLL reference ?

Any help much appreciated. Many Thanks !

[Diamonddrake]

Its more likely that you have an assembly loaded that relies on the older version of that dll. Don't forget that your project references are important, but many dlls make references of their own that you don't see.

[C#Jonathan]

Thanks for your help - you were right I've rebuilt the offending dlls and all works well now - Thank you !