Well, we would certainly have to have the file, to be able to say more.
The path ("c: config \ msi") doesn't seem to be complete - you are re-typing it from the Simple User Interface window, right?
If possible, please go to the program settings and turn on the creation of the Report file; make sure the "Hard errors" and "Soft errors" items are checked, and use "Text file" as the type. Then, run the scan again. avast! will create a text file in the selected folder (by default, it's C:\Program Files\ALWIL Software\avast4\DATA\report\Simple user interface.txt). So, if the error appears again, it should be logged in the report. Just open the report file e.g. in Notepad, find the item and copy&paste the line here.
Thanks!