First put an 8.5 x 11 24lb sheet in the tray and see if you can copy onto it. If not, tray 5 has a mechanical problem and will require a service call. If it works then your print settings are probably wrong. Make sure that the size is correct. If its 8.5 x 11 SEF or LEF from the driver and application and that it is the same on the machine when you first load the labels into tray 5.
The problem is only with "Labels" or any other form of stock? Are you able to set the bypass tray settings to "Labels" or is this when the error occurs? Are you using new Labels or are these the same ones from before?
When trying to print labels from the bypass tray (tray 5) an error comes up regarding that tray. I've checked the settings to make sure they show tray 5 usage and they do. Problem message ends in "contact your administrator"