Logisim Combinational circuit
The output on the right shows "error" because at least one input of the gate feading it is erroneous, too. This is true for other gates in your circuit also.

Most probably this happened (you didn't tell us):

While editing, you made some error that led to wires carrying "error", shown in red with the value E. Perhaps the simulation even stopped, and it might have told you.

To recover, reset the simulation, starting it again. You will find the commands in the menu.