Prebuild event in Visual Studio replacing $(SolutionDir) with *Undefined*

I believe the problem is documented here moved here and looks like it might be a bug in visual studio, but I'm wondering if anyone knows of a workaround.

Basically I have the following two lines (among other things) one right after the other in the prebuild event.

"C:\WINDOWS\Microsoft.NET\Framework\v3.5\MSBuild.exe" /p:configuration=Release;platform=x86 /t:rebuild "$(SolutionDir)Folder1\Project1.csproj"

"C:\WINDOWS\Microsoft.NET\Framework\v3.5\MSBuild.exe" /p:configuration=Release;platform=x86 /t:rebuild "$(SolutionDir)Folder2\Folder3\Project2.csproj" 

The first one succeeds and the other fails saying that The command ""C:\WINDOWS\Microsoft.NET\Framework\v3.5\MSBuild.exe" /p:configuration=Release;platform=x86 /t:rebuild "*Undefined*Folder2\Folder3\Project2.csproj"" exited with code 1..

Edit:
Figured out the problem was that one of the other projects with the same line as it's prebuild failed, since MSBuild itself doesn't know about the macros.

I fixed this by replacing all $(SolutionDir) with $(ProjectDir)..\.

It was due to MSBuild running each project independently, and thus not the solution. It worked fine in VS2010, but not on the build server.

Wasted a lot of time to find perfect solution for this problem. Use Directory.Build.props.

In your sln location folder create a file with name Directory.Build.props and put this code inside:

<Project>
 <PropertyGroup>
    <SolutionDir>$(MSBuildThisFileDirectory)</SolutionDir>
 </PropertyGroup>
</Project>

This file will be automagically picked up by all your csproj files and will define (SolutionDir) property.

Allan's answer is exactly on the right path, but if you want to move to parent directory of the ProjectDir, or the $(ProjectDir)..\ output is going to be a string, you need to perform the 'go to parent directory' operation in msbuild.
Here is how you can achieve this:

<PropertyGroup>
  <TrimmedDir>$([System.IO.Path]::GetDirectoryName($(ProjectDir)))</TrimmedDir>
</PropertyGroup>

This code will set the parent directory path of the ProjectDir to TrimmedDir variable. [System.IO.Path]::GetDirectoryName() performs this operation.