'Printer index out of range' - Odd little error that occurs from time to time and not one that we have found the ultimate fix for yet BUT ..
Try the below:
A) Has the user saved the job before trying to print? Helps.
B) Try logging out of eCargo and then back in again. If a printer has been moved or adjusted sometime an instruction gets confused.
C) Something that often works for one of our business managers is:
When it happens we get the user to go into their list of printers, right click and go into the properties, then click the ok button (you don't need to change anything) and try printing again.
D) Shut down the PC and bring back up again. The printer configuration may need to be reset.
Hopefully one of the above will solve the issue for you. If it doesn't please contact our help desk.