Cannot open app designer

After I worked on App designer for a longtime (4-5 hours), I got an error. When I tried to re-open, it showed nothing but the main window. Have anyone come across this problem? How can you fix it?

Thank you so much!

[Chris Portal]

What OS are you running?

If you do the following:

cd(prefdir)
load('matlabprefs.mat')

What are the settings returned by:

Preferences.appdesigner

[Dave Morrissey]

Do you remember setting the HandleVisibility property on any component to be something other than the default of 'on'?