I am following a video tutorial from my university on how to create a differential housing and I have followed every step exactly, yet when I go to put a fillet on a certain feature I am getting an error about the fillet being too large for the surrounding area. Yet the instructors works fine for some reason. I have triple checked I have done everything exactly the same, but for the life of me I can't apply the fillet. I am using Solidworks 2017, although I am not sure what his version is. I have also attached my file. Looking for any advice here on what I can do to get this fillet to work.

The screenshot below is from his video. The fillet radius is 2.5mm. Fillet size is constant, symmetric and circular.

The screenshot below is from my attempt.