Unable to disjoin domain

Several weeks ago a workstation was experiencing really slow logon/off times. When I tried to disjoin it from the domain I was told "The following error occurred attempting to unjoin the domain: the specified module could not be found". Now what? It turned out that w32time.dll was missing from the c:\windows\system32 directory. Because it was missing, the Net Logon service couldn't run. The Net Logon service is essential for interacting with a domain.