Have you tried to hand in a file, and gotten a message something like:
Error Copying01.png

And on the HANDINS folder, the file suddenly contains no data

Your file has been BLOCKED by Windows!
Files downloaded from external sources like GoogleDrive or your cellphone camera may be tagged as suspicious, and be "blocked" from moving around the network security software.

The solution is easy:
Error Copying02.png
- RIGHT MOUSECLICK the file and bring up it's PROPERTIES
- Look at the bottom right corner of properties, and click the UNBLOCK button
- Click the APPLY and OK buttons, and you're done

Your file should now be easy to move to the handins folder!