I get an "application error" when using ECCOext.  And, do not get the error using the regular ECCO program.  The errors occurs when using the standard either the ECCO default template using ECCOext or the new default template. The error (An application error has occurred. Please exit Ecco and restart) occurs when trying to drag a name from the phone book to either the weekly or monthly calendar. Dragging to the daily calendar works fine, however.  And as mentioned, if I open any ECCO files, either the original default templates or the new EXT templates with the original ECCO program, the error does not occur, and I am able to drag and schedule to weekly and monthly calendars just fine.
 
-David Smith
 

try with calendar in weekly GRAPHICAL view..  (also, my own test was with notepad, not phonebook, but likely same..)
 
Edited:

 
technically it is "summary vs. detail viewing"
 
shortcut key is Shift + F10
 
 
(no effect in daily view other than resetting the view)

dragging marked item to the blue box (date) causes error gen on my 4.0.0.3
 
you can drag & not get error,  same ext. vers ?

funny,  I was using 4.0.0.1 in my first tests, and thought maybe the .3 was different, and explained your results!