AMOS - Confirmatory factor analysis - why the zero's on my error terms?

I am trying to complete a confirmatory factor analysis in AMOS (255 subjects, 57 variables, 3 factors). I understand why AMOS automatically sets the regression weights of error terms to 1, however I am not sure what the zeros appearing above every error term are (a 0 with a small 1 to the bottom right). What are these terms? Will they be affecting my model? Can I change them? Simply deleting them all stops the model from running.
Apologies if this is an obvious questions but the AMOS user guide, AMOS help and many online tutorials and searches have not provided an answer.
Thanks in advance for any help.