Mysterious "Could not copy file" message during startup

[Brian49]

During system startup, just after the GRUB menu page, a message appears near the top of my screen saying "Could not copy file: no such file or directory". The file in question isn't identified, nor can I find any mention of the glitch in any of the system logs. How can I track this down, please? The "missing" file doesn't prevent me getting to my desktop or carrying out normal activities once there, but it's a bit disconcerting so I'd like to find out what's going on if possible. I've tried profiling GRUB and then running update-grub, but the message is still there. Running LMDE Xfce tracking Debian Unstable, with most updates installed. Many thanks for any kind advice.