goodmornin',
I have the AdAware free version, running on XP.
since "upgrading" to the 2007 version, i too have had regular "TVirtualStringtree" problems.
With the "free" version, there is no access to support (though the "pop-up" error notification requests a report to Lavasoft be made) beyond the forums.
reloading the program has not helped. removing, downloading AND reloading the program has not helped.
however, i have noted the problem consistently appears if:
1) stop scan BEFORE it finishes
and/or
2) when "Removing".
a) when selecting item listed then clicking "remove", a SECOND box will usually appear waiting 'to be selected'.

do NOT select the second selection box OR click "remove" additional times. to do so WILL cause the pop-up
error notification.
c) if the pop-up error notification APPEARS, do NOTHING until the number in the tab/folder (i.e. CRITICAL)
has reached ZERO. THEN close the pop-up error notification box.
d) closing the pop-up error notification box will cause the AD-AWARE program to close itself.
-stev