Backup to USB drive fails

[barkpro]

Netgear Ultra 4 with 2 x 2TB drives using <500GB.
Back up to 1TB Lacie rugged is failing.

Error encountered copying data from source path ==> /USB_HDD_2/ due to unknown reason. Please see log.
cp: cannot create directory '/USB_HDD_2/./Fitton Insurance/5873 Fitton Website Layout ': Invalid argument
cp: cannot create directory '/USB_HDD_2/./Willis/5856 Willis AKSA:2fKAL Summary of Cover Flyer': Invalid argument

This has been an intermittent problem, backup gets stuck on certain file (i think), if I leave it for next day backup, same files noted. If I remove the noted files, backup will complete next run.

Please advise.

[StephenB]

How is the USB drive formatted?

There are restrictions in naming that are specific to each format. For instance the : in '/USB_HDD_2/./Willis/5856 Willis AKSA:2fKAL Summary of Cover Flyer' isn't allowed in FAT32 or NTFS.