I’m in the process of updating a bunch of old Visual Studio 2003 projects and solutions to, well, something a little newer. I found this odd behavior issue where there were some references that were marked to as “Copy Local” and that would work fine in a Visual Studio build, but when run from MSBuild, the references weren’t getting copied correctly, which would cause unit tests to fail and such because things weren’t where they should be.

A little Googling led me to this forum post which basically boils down to:

Go through your projects in a text editor and look for references with <Private> tags in them. Like <Private>True</Private> or <Private>False</Private>. “Private” is a synonym for “Copy Local.” Somewhere in the actions MSBuild is taking to locate dependencies, it’s finding your dependency somewhere else and deciding not to copy it.

What I ended up donig is going through each converted .csproj file and removing the <Private> tags manually. Rebuild, and everything works in both Visual Studio and MSBuild. Once you’ve got that working, you can go back in and update things to where you think they need to be, and when things start failing, you’ll know exactly where the problem is.