Simple concept: After In-place upgrade stsadm.exe crashed

[Question]: why stsadm.exe gives an error after in-place SharePoint 2010 upgrade?
Unhandled Exception: System.MissingMethodException: Method not found: 


[Answer]: You have an old path for stsadm in the environment variables. Change it to C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\BIN\