Error code 02 when using NetZero software

Hi,
I was starting NetZero when this error message popped up on my screen (see below for the screenshot).
I wondered why the message said that NetZero software is already running since I hadn’t started it yet.
I had tried rebooting my laptop, but the error didn’t seem to go away.
Any suggestions to fix the problem?

Problem Starting NetZero
The NetZero software is already running.
You must close the software before restarting it.
Error Code: 02
