Im getting the same issue, here is a c&p from the terminal
The following packages will be DOWNGRADED:
arachni
999 upgraded, 93 newly installed, 1 downgraded, 0 to remove and 0 not upgraded.
Need to get 1,492 MB of archives.
After this operation, 1,090 MB of additional disk space will be used.
Do you want to continue? [Y/n] y
Err:1 http://deb.parrotsec.org/parrot parrot/main amd64 base-files amd64 1:2019.01parrot1
404 Not Found [IP: 2604:a880:cad:d0::5ed:5001 80]
Err:2 http://deb.parrotsec.org/parrot parrot/main amd64 bash amd64 5.0-1
404 Not Found [IP: 2604:a880:cad:d0::5ed:5001 80]
the iso is still there https://www.parrotsec.org/download-security.php
maybe you should grab the latest 4.5 iso and use that instead of updating from 4.1 because everything works fine here