You're getting the error because the gateway doesn't have conditions for none of the checkboxes to be checked.  An inclusive gateway acts as an and/or decision and the form submission does not match any of your conditions.

so what should I add?

If you don't want either of the paths to be the default outflow path, create another path from the gateway to your End and put in conditions for that path where everything is unchecked.

what would the condition be "not checked"? 

!="checked"

That is the condition I have for the Assistive Technology and DHH. I am getting the error when none of the boxes are checked

You aren't accounting for some possibility in your conditional rules. The solution is to define all possibilities and account for all of them in your conditions. This becomes easier by making one of them the default, which I strongly suggest, since that would've prevented this from ever happening to begin with.

that's what I did previously but it did not work, apparently I was using the incorrect gateway. changed it to Exclusive and made one the default. think it is working now.. thanks!!

Unfortunately, it is still not working. What condition should I put so that when none of the boxes are checked, the process will still work?

You haven't made clear what the desired outcome is, so this is a guess:

The conditions for Assistive Technology should be when any of the Assistive Technology boxes are checked. The conditions for DDH should be when any of the DDH boxes are checked. The conditions for Notify Student should be default.

This is with the assumption that it should only be routed through one of these branches.