you have to reinstall the v 2018, open your files that was opened and saved in v 2018 and then save them back to v 2017 and close the drawing, repeat for all the drawings you have from v 2018 and after that un install v 2018.
Then they should work i 2017
V18, V19, V20, V21, 2015/ 16/ 17/ 18 Pro. Platinum
Deluxe V20, V21, 2015/ 16/ 17
Windows 10 Home Premium 64 bit, 32 GB
NVIDIA Geforce GTX 780m, 1 GB