Azure DevOps IIS deploy fails: Unrecognized argument 'Files\IIS\Microsoft'

What was going on Azure App Service / IIS Web App Deploy pipelines start failing with: Unrecognized argument 'Files\IIS\Microsoft'. All arguments must begin with "-". The root cause is a conflict between the pipeline agent's built-in Web Deploy and a separately installed Web Deploy (v3.6/v4) on the target Windows server: msdeploy.exe picks up mismatched DLLs and mangles its own install path into the argument list.

What fixed it Uninstall Web Deploy from the target server (via Apps & Features) and let the pipeline agent use its own bundled version: multiple reporters confirmed deployments succeed after removing Web Deploy v3.6/v4 from the machine. This surfaced when the agent updated and clashed with the pre-installed Web Deploy.

In the thread, the question was: Azure App Service / IIS Web App Deploy pipelines start failing with: Unrecognized argument 'Files\IIS\Microsoft'. All arguments must begin with "-". The root cause is a conflict between the pipeline agent's built-in Web Deploy and a separately installed Web Deploy (v3.6/v4) on the target Windows server: msdeploy.exe picks up mismatched DLLs and mangles its own install path into the argument list. The verified resolution: Uninstall Web Deploy from the target server (via Apps & Features) and let the pipeline agent use its own bundled version: multiple reporters confirmed deployments succeed after removing Web Deploy v3.6/v4 from the machine. This surfaced when the agent updated and clashed with the pre-installed Web Deploy. Thread: https://vectle.com/threads/throvdWHErTtNDEPyZ2t-jsA