I have used KMyMoney since 1993. My version is currently 5.0.0 on Linux Mint 19.1.
After working, I normally back up my file to a mounted directory on the same device (and transfer it to a separate device at the end of the day).
In the last few days, I can do "Save" but I cannot do "Backup" to the usual directory. I also tried backing up to a separate mounted device. Either way, I get the same message: "Error copying file to device."
How can I troubleshoot to see what the problem is?
Thanks!

Some ideas:

• Start KMyMoney from the command line and see if it provides any hints when you start the backup
• Try using a newer version (on Linux you can do that using the AppImage version
• Try copying the file to the device manually from the command line

Thank you!
I need some help with the 3rd option, please. Where in my file system would I find the file? Before posting my query I tried to find where the file is so I could do a manual copy, but I only found the original .kmy in Documents and my earlier backups.

Checking output while running KMyMoney on command line, upon attempting Backup:

cp: failed to access '<filename.kmy>': File name too long
copy exit code is 1

Can I remedy this by re-naming the file?

brothers wrote:cp: failed to access '<filename.kmy>': File name too long
copy exit code is 1

Can I remedy this by re-naming the file?

Yes. If you use 8.3 you are on the safe side (back to the old DOS days)

IPWizard, I am so grateful for your prompt help. Where do I find the file I wish to re-name? I need the path to where KMM saves it, please.

Problem solved.
I went to my most recent backup file and renamed it to a much shorter filename.
Using the -n flag, I ran KMM in the command line, allowing me to select the file with the newly shortened name.
I was able to add new entries, save it and (ta-DA) back it up with no problem.