Qt moc error 1 - what does it mean?

The solution was annoyingly simple. I had a folder structure that put spaces (illegal characters) in the file path. I put underscores instead of spaces and it built fine. I would think the moc pre-processor could handle spaces in file names, but apparently not. I feel foolish, but at least the problem is solved now.

Hopefully this solution can help someone else.

Click on "compile output", scroll up and click the red line.

In my case the Red line was saying: You cant define an integer value in private slots..

Under the qt creator window, in "progress details" section, there is a button named "compile output" (button number 4). Errors are explained there with red font. Click it and scroll up.