update install package error

[bats059]

Hi, I'm trying to update to 5.2.1 on my pi, but I keep getting errors. Copied manually from the pi's screen, they are-

dpkg-deb (subprocess):decompressing archive member: internal gzip read error: '<fd:4>: incorrect data check'
dpkg-deb: error: subprocess <decompress> returned error exit status 2
dpkg: error processing /mnt/music/subsonic/subsonic-5.2.1.deb (--instal): cannot copy extracted data for './var/subsonic/transcode/ffmpeg' to '/var/subsonic/transcode/ffmpeg.dpkg-new': unexpected end of file or stream

I have tried it with files from two separate mirrors, one in Australia and one in the UK, just in case one was corrupt, but no difference in the errors with either file.

Iam logged in as root (actually, sudo -s) and used the command

dpkg -i {path to file+file}

to install.

Am I missing something, making a mistake, or is the .deb file actualy corrupt?
If so, where can I get a known good file?

Thanks, Ken.