Answer: This is ATO side validation. 

Please kindly check if you can see the form is lodged on ATO portal, if yes, kindly mark the form as lodged in LodgeiT. 

Guide: How to "mark form as lodged"

This error triggers when the ATO rejects the return due to a return already lodged for a particular year for the TFN. In this case, please check the ATO portal to see if a return for the same year was lodge.

Other workaround:

Please try to remove the ABN from the return and attempt to lodge again. If you have attempted to relodge and still receive the error, please call the ATO, that is the fastest way and they can fix such issues online. If it didn't help - please let us know and we'll contact ATO tech team for them to investigate. Note that, it will take a week for them to response. ATO phone 13 72 86 Fast Key Code 3 1 2.

For 'future forms', refer to ATO's instruction Here

Before that, make sure to unlock the form first.

 Remove the ABN from client's "settings"

Then re-open the form and make sure there is no ABN on form, then try to lodge again