Cannot export files to external drives

Have iBook G4 with OS X 10.5.8

1.2 Ghz PowerPC G4. Memory 512 MB. 74.5 GB hard drive, 64 GB available.

I am trying to export files & folders onto either a memory stick or an external hard drive.

I get "The item XXXX cannot be copied because there is not enough free space." Both for tiny files & big folders.

However, the target drives do have plenty of space. They also work OK on an alternative Mac. I tried reformatting a memory drive as well without joy?

What is preventing the iBook G4 exporting files?

Thanks