I may have partially "fixed" it again by making my wife's account administrative. Avast does run if I do that, but I am told that it is not a good idea. Also, this does not fix the guest account. Making that administrative is really a bad idea.
I copied some of the error message:
Microsoft Visual C++ Runtime Library
Assertion failed!
Program:C:\Program Files\AVAST Software\AvastUI.exe
File: .\CrashHandler.cpp
Line: 43
This topic has appeared in this forum before. One was June 24, 2012. I did not see a resolution to it.
Any chance it will be fixed in the next release of Avast?