Hi Mathieu
Thank you for your reply:
I will screenshot the errors to show you the details more.
I chose one student to delete the submission:
I clicked on the option and confirmed it :
It didn't work so I deleted purged the cache
I did it a couple of times:
But I got the same error.
However, last time after purging al caches it didn't give me the error but nothing happened.
Your help is much appreciated.