The volume is the wrong format for a backup.

what does this mean? I can no longer drag photos into my stick

What format is your flash drive using? If it's formatted to NTFS it will be read only and you won't be able to write (drag photos) to it.

Sorry as a total novice I dont know what it means ! It is a new stick, info says 16.01GB SanDisk Cruze. I tried formatting in MS-Dos (FAT) as instructed but no good, I used it twice last week successfully - but after deleting some old photos yesterday it refuses to work and brings up the message'The volume is the wrong format for a backup.'

It sounds like your SanDisk Cruze is corrupt. Those flash drives are pre-formatted as FAT-32 and designed to work for both PC and Mac.

Plug the drive into your Mac and open Disk Utility (Applications, Utilities, Disk Utility.app). Erase the drive first and then format it to MS DOS. Make sure the "MBR" scheme is selected. (should be automatic) If the drive will not format, it may be defective and should be returned for a new one.

This may well have happened if you have been "pulling" the stick out without properly dismounting it.

Watch out for foreign characters in file names

Hi all...
Having come across this problem a few times myself, I thought I'd post this reply just in case none of the above solutions don't work for you. Although the above are all valid, there is ANOTHER reason other than these that you may receive this error even if your drive is operating perfectly: Foreign characters in file names, i.e. extended character sets.

If you're trying to copy a file to an external drive / memory stick that is formatted as NTFS for example, the file system may not support these; and YES you CAN copy only NTFS drives if you're running the appropriate third party software on your Mac to do so (I'm using Paragon NTFS for Mac OS X).

Example of a problematic filename: Felix Kröcher - Scheint.m4a <-- Notice the double dotted 'o' in 'Kröcher' (assuming this editor supports display of the character set).

Hope this helps out someone in the future as it had me a little perplexed for a while.
Regards, Adrian.

Nice tip. That never occurred to me. I rarely deal with filenames having the extended character set.

Not sure that is always the case Sly. We routinely copy Asian language (non Roman character set) files back and forth from our Office iMac to flash drives and external drives without any problem whatsoever. There may be certain characters which are not compatible, but that usually shows up as an error in a file name.

That certainly is more like what I would expect. I've been trying to pin this down a bit better but not having a lot of luck.