I solved the problem, but at the expense of Dell's notification alert program.   The perlib and perfnet error indicators in Event Viewer went away when, at the recommendation of a program called Ultimate Troubleshooter,  I removed the Dell support.exe program and, with it, notifyAlert, from Startup in Msconfig.  The program was listed as DwlClient. 

I worked around the loss of the notification program by putting a shortcut for support.exe on the desktop, where I can run it periodically  after all of the startup programs have been loaded.  Support.exe is in C:\Program Files\Common Files\Dell\EUSW. 

If Dell has a better way around the problem, I would like to know it.