Please check the following -

a. That the client is in your ATO Portal & you have permission to lodge on their behalf

b. That the ABN & TFN are recorded correctly in LodgeiT

c. That the ABN has not been cancelled. If it has, please remove it from LodgeiT.

d. Possibly there is a Branch Code. If so, attempt to replace 001 with 002 at Settings -> General.

e. If it's your first lodgement, check your Tax Agent details  e.g. Tax/BAS agent number