I know Mint is Debian-based. I received my Raspberry Pi yesterday, and have been configuring it today. It, too, is Debian-based. However, /var/log/messages does exist on Raspbian.
Are you sure you are in the /var/log directory? Try this:
grep -i mouse /var/log/messages
rather than changing to the right directory, this will point the grep to the right file no matter where you are. Don't forget the slashes.
No such file or directory
I'm gonna do a little research on my system board. I'm beginning to wonder if something with the motherboard or cpu cooling fan is an indication of the problem because the mouse only locks up when the cpu cooling fans kicks into a higher speed.