Why is the start button grey on some LabTutor panels and not others?

 The "allow data changes" box must be ticked on any LabTutor panel (master or alias) for students to collect data.

This can occur when modifying an experiment in LabAuthor.  All buttons will appear to work when previewing in LabAuthor but will be inactive and grey when the experiment is installed.
To correct this, open the experiment in LabAuthor, select the panel properties and tick the "allow data changes" box.  Save the experiment, save the installer, and install on your server.