update problem - some files not found

[Bill Stanley]

Hi,

I realize that this is a Mint problem but this forum offers good advice 
that I can't find elsewhere.

I am trying to update Mint Linux 21.3 Virginia using Update manager.  It 
partially worked and updated some packages but it failed to install some 
security updates because it could not fetch 3 files. The error messages 
clearly indicate that at least 3 files could not be found.  The error 
messages are...

*************************************************************************
W:Failed to fetch 
http://packages.linuxmint.com/pool/upstream/f/firefox/firefox_124.0.1%2blinuxmint1%2bvirginia_amd64.deb
   404  Not Found [IP: 68.235.39.11 80]

W: Failed to fetch 
http://security.ubuntu.com/ubuntu/pool/main/t/thunderbird/thunderbird-locale-en_115.9.0%2bbuild1-0ubuntu0.22.04.1_amd64.deb
   404  Not Found [IP: 91.189.91.82 80]

W: Failed to fetch 
http://security.ubuntu.com/ubuntu/pool/main/u/util-linux/bsdutils_2.37.2-4ubuntu3.3_amd64.deb
   404  Not Found [IP: 185.125.190.39 80]
*********************************************************************

How can I solve this problem.  I checked the internet and found these 
files but am also not sure that the files I found are legitimate.  One 
can not be too careful when updating security stuff.  Maybe this 
indicates that my system has been compromised?

Thanks for any help in advance.
Bill Stanley