Result of expression 'Titanium.UI.createButton' [] is not a function

When loading a window, I'm getting the following error:

[ERROR] Script Error = Result of expression 'Titanium.UI.createButton' [] is not a function. at userHome.js (line 142).

Nothing changed in the code. I recently upgraded the SDK version. I've already tried cleaning the application, which in the past has fixed similar issues. Here's the code in question.

var classButton = Titanium.UI.createButton({
            right : 5,
            width: 175,
            height: 45,
            title : 'Join live class',
            row : x,
            section : 0
        });
        classButton.addEventListener('click', runFunctionA);
        row.add(classButton);

hi,

if you upgraded the sdk and did not restart the Ti Studio then do it first.

have you cleaned the app from project menu..?