When the assertion hits and you pressed "Recommencer", press ALT+7 (or in menu pick View->Debug Window->Call Stack. A docked or floating call stack window should be displayed.
Read the list in the call stack window from top to bottom and imagine that each call is a function call. Find the first line that starts with a class name or global function name of your project. Double-click on this line.
The code line right before the displayed line is the one that finally caused the assertion. Maybe it is a ShowWindow or something like that. Try to find out for what reason this command fails.