IllegalCastException on MainWindow.visible = false

In my event, for years I’ve had the line:

MainWindow.visible = false

MainWindow is, as you may have guessed, the main window of my application, and I’m not ready to show it yet. Today with 13R3 this line is throwing an IllegalCastException. It also throws if I try MainWindow.left = 0 or try to touch any other part of MainWindow. I’ve tried just setting MainWindow.visible to false in the IDE to begin with, but then in other sections of my app (namely, after a password is entered in another window that comes up first) any access of anything inside MainWindow throws the same IllegalCastException.

MainWindow IS set as implicitInstance, and is currently set to visible in the IDE. Did “MainWindow” suddenly become a reserved word or something? What else could be going on here?

Lets see …

IF you have an implicit instance then
MainWindow.visible = false
is going to create one just to set it not visible

Beyond that there’s nothing wrong with the line of code so something else is going on
I just did this in R3 with a new project so …

Yes, something was definitely going on. MainWindow was an external item. I changed it to be internal, and suddenly the problem went away.

There have been several issues I’ve run into today that were caused by using external items… I’m bringing everything internal to this project now in the hopes to cut down some issues down the road. Possibly I’ll have to round-trip some of these items to be external again for use in other projects… but I’ll cross that bridge when those deadlines loom instead of the current one I face.