Project file contains ToolsVersion="4.0", which is not supported by this version of MSBuild.

Question

How do I get rid of this error, I am using Visual Studio 2008 because 2010 wouldn't open some of my VB Projects.

Answer 1

A VS2008 project file starts out with

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="3.5" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003"&gt;
  <PropertyGroup>

where the ToolsVersion indicates the .net framework tools version. VS2010 uses .net 4, so clearly has made the corresponding change in its tools version.

I would expect that opening your project files in Notepad and resetting the tools version to 3.5 will clear that issue. Whether there are other backwards incompatibilities lurking, I couldn't say.