AppDesigner won't run or save: "Too many output variables"

When I open a brand new App Designer, I can't even save it because the error "Too many output arguments." appears. Even though I haven't made any changes to the file yet. What do I need to do to be able to save an App Designer file?!

[Walter Roberson]

As an experiment try

restoredefaultpath; rehash toolboxcache

if it starts working again, the implication would be that you have something on your MATLAB path that is interfering with MATLAB's built-in functions.

[Mitchell Tillman]

This worked thank you!

[Walter Roberson]

Quit MATLAB and restart and use pathtool to have a look at which non-Mathworks directories are in your path. Somewhere in one of them is a function that is interfering with using App Designer.

[Mitchell Tillman]

Do you have any idea what types of things may interfere with App Designer? I have no idea what I'm looking for. I've had to use the method you suggested repeatedly, despite only adding a couple of subfolders to the path.