@FellippeHeitor Some more info regarding this. The other source I am switching around with is the whole display (which has the $DEBUG IDE on the right hand side, whereas what I am testing is on the left hand side, sometimes right hand side, but mainly the top of screen).
The $DEBUG error never seems to occur with _FREEIMAGE s&, ONLY with _FREEIMAGE t&.
Note that the t& source relates to only the very top of the display (non-overlapping with $DEBUG IDE).
I am beginning to understand the conflict - at present only one monitor used - if I added a second (low quality) monitor, is it possible (and how), to have $DEBUG IDE only display on the second monitor
When $DEBUG reports the error, after about a second or two, it carries on until the next _FREEIMAGE t& and so on...
The breakpoint occurs when the program is accessing the very top of the display.
t& = _NEWIMAGE(wdth, hght,32)
SCREEN t&
...
if s& <-1 then _freeimage s&
s& = _SCREENIMAGE
_SOURCE s&
...
IF t& < -1 then _FREEIMAGE t& '
This is line xxx_SOURCE t&