also check that your exterior walls and interior wall have the same "group" assigned. walls with differing groups will not clean up.
selact a wall, right click to pop up the shortcut menu, select "wall modify"
note the "group" style. Then select your exterior wall and make sure that the same "group" is applied.
Other things to check: in the "options" dialog box, go to the "AEC drawing defaults" tab and set wall cleanup radius to 0"
Still in the options dialog box, go to the "AEC performance" tab and make sure the box "Never clean up wall intersections" is NOT checked.
Hang in there, as 42 said, the learning curve is VERY steep!
I went from Acad14 w/softdesk s8 to ADT3.3 2 years ago, and am still learning new things every day. I was self taught on autocad and softdesk, but had to break down and go to a training class for ADT3.3.
I would highly recommend it , if you can get your employer to spring for it!