The Problem
I recently had a customer who’s Azure DevOps Pipelines BizTalk 2020 build had suddenly started to fail. They said they had not altered their BizTalk solution, or their build process.
The Analysis
Turns out the issue was that the operating system on the VM that hosts their self-hosted Azure DevOps agent had had a update. This update it seems had updated the version of MSBUILD shipped with Windows. Making it the newest version, newer than the one shipped with Visual Studio 2019.
This could be seen clearly when comparing the successful and failing BizTalk builds. The path to the MSBUILD.EXE file had changed.
The Solution
So, the problem was that the MSBuild task in the Azure DevOps pipeline was set to use the newest version of MSBUILD on the agent.
The fix was easy, change this setting to make sure it used the version of MSBuild installed as part of Visual Studio 2019, the version configured for Biztalk 2020.