Hello everyone,
in the assignment of C1W2 i got an error from the grader
“Sorry, your submission was incorrect. Please try again. Invalid control character at: line 731 column 18556 (char 507890)”
The notebook is working and the results are looking fine.
Can someone give me a hint how to fix it?
Many thanks in advance!
Check if you hardcode something, there should be some kind of error for sure! Or maybe you deleted some part of the code or comments you are not supposed to tamper with 
Did you download the notebook, work on it via some other platform, and then upload it back to the course?
No, i did not download and modified it beside the coursera platform.
As a next step i will double check if i messed up any comment.
I don’t think that i have hardcoded something.
Hey there! I had the same issue with other course’s labs, and the following method worked for me. If your problem hasn’t been solved, try backing up your answers, restoring the initial version of the notebook from the checkpoints section, and manually typing your answers into the cells again. I hope that helps!
Thank you all for your replies!
Finally solved the problem. Started a new, fresh workspace and copied over my previous solutions. Here i found that i left a “,” in a wrong place like
nn.sequential(nn.xxx(),)
All tests were passed but the grader got confused about the last “,”.
Honestly i think i haven’t found this if i didn’t start a new workspace.
Problem solved. THX!
You’re welcome! Happy to help 
Thanks for your report.