Here’s a clear, step-by-step write-up for fixing DISM Error 87 (typically “The option is unknown” or “The parameter is incorrect”):

If a particular switch doesn’t appear in the help list, it doesn’t exist in your version of Windows (e.g., some switches are only for Windows PE).

To check health:

DISM /Online /Cleanup-Image /CheckHealth

8. Appendix — Useful Commands Reference

Sometimes, the spacing is perfect, but the error remains. Here are the common hurdles users face:

This command bypasses many CMD-specific syntax issues.