@FreyMiggen, I’m not sure what this is. We’ve had a learner run across a similar error in the past, but their problem mysteriously resolved itself when they tried again (see Week 3 assignment: zero grade - #6 by terikihuan)
One thing to try - for some of the GANs assignments, the images can get quite large, which can cause issues in the grader. To minimize the size of your assignment’s image, open the assignment and select Kernel-> Restart and Clear Output. Then Save (File → Save and Checkpoint). Then try “Submit Assignment” again.