Musescore won't install on Intel 64 bit CPU PC, help please

Hi All,

I've recently come across Musescore and really want to try it out, but I'm experiencing what looks like a 64 bit specific install problem. I've searched these forums, but my problem seems not related with the few other 64 bit specific install problem thread I've found.

I'm trying to install onto the 64 bit version of an Ubuntu / Debian based distribution called Linux Mint.

The following command:
"sudo apt-get install musescore"

produces this error:
"Err http://archive.ubuntu.com/ubuntu/ precise-updates/main libqt4-scripttools amd64 4:4.8.1-0ubuntu4.2
404 Not Found [IP: 91.189.92.156 80]
Failed to fetch http://archive.ubuntu.com/ubuntu/poo...u4.2_amd64.deb 404 Not Found [IP: 91.189.92.156 80]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?"

I've also tried two alternative methods.

Installing from the official website:
http://musescore.org/en/download

I'm getting this:
"Some of the packages could not be retrieved from the server(s).
Do you want to continue, ignoring these packages?"

I'm not man enough to choose yes, so I choose no and get this:
"W: Failed to fetch http://archive.ubuntu.com/ubuntu/poo...u4.2_amd64.deb
404 Not Found [IP: 91.189.92.201 80]"

The second alternative method is this Software Manager GUI thing, which I presume may be a frontend to apt-get, and which silently aborts the install task.

This is well beyond my skills, which can be described as average Linux user.

I would very much appreciate any advice and thank you in advance.

With best wishes for the New Year.