Thanks for reaching out to us with this one, I'll try my best to help you troubleshoot.
There could be a number of reasons why you cannot mark a BAS as lodged in QuickBooks.
First off, have you connected your QuickBooks to the ATO via e-lodge?
Have the previous BAS's been lodged before the one you are trying to lodge now (remember they must be done in chronological order).
What is the error message you are getting? Could you please type it out word for word so as we can understand exactly what the situation is?
I'd love to help you fix this.
Attached is a screen shot of the error message I am getting. I have lodged all previous BAS's online through the ATO Business Portal. I have also connected my Quickbooks to the ATO via e-lodge but have not used this function previously as I lodged it through the ATO Business Portal. I have a feeling it is coming back with the error when I try to mark it as lodged as it is already registering I have lodged it on the portal? At the moment I can't see the next BAS which is due to be lodged shortly as the previous one is showing up still in my to do list with the "prepare BAS" button. Have you seen this before? Your help would be appreciated, thanks Ilona