Problem copying some files only

After doing a fresh backup of documents from one external drive to another, although 4337 files within the various folders have been copied, I get a log message that 4 have not been able to be copied.

At first, I presumed that it was a Comodo Backup problem, but then to check this, I tried to simply copy and past these files from one HD to the other. In one case, doing the latter, I got a mesage that the file name of the webpage was too long. I find this strange. Why did I have no trouble copying this in the first place from my laptop to the first HD? Anyway, I shortened the file name and was then able to copy and past it to the backup HD.

The there was this webpage:
“The Brandenburg Concertos and Musica Florea - Český rozhlas D-Dur”
Comodo BackUp gave me the same error message I have mentioned above, but in this case, after Comodo could not copy it, I was able to copy and paste it manually to the backup HD.

OK, it’s got foreign script, but I can’t see anything else unusual here. The file name’s not that long…

I’m back again after shortening the file name to this:
“The Brandenburg Concertos and Musica Florea” and it’s copied correctly.

All is well now, but what is troubling is that I cannot see a clear pattern in this, and in any case, how will I know what file names Comodo Backup will accept in the future when saving files to the laptop/pc?

Thanks,
Andrew.