I am trying to load the web source project (letsbuild_web) into Visual Studio 2005 and it wants to convert but I get a conversion error (ERROR: Unable to parse project file LetsBuild_Web.csproj).

Do you know what the problem could be? Do you have a VS 2005 version?

Answer

The version is for VS2005 sp1. One thing that may explain this is that the project uses the "Web Application project model" introduced in Get Visual Studio 2005 SP1 described like this:

Web Application Projects
Web Application Projects provide Visual Studio 2005 with a Web project model similar to the Visual Studio .NET 2003 model.
Note: Visual Studio 2005 Service Pack 1 incorporates Web Application Projects.

Read more about it here