Why can I not move a .dmg or .iso to an external HD?

I have a .dmg file that i want to put on my external to back it up but when i attempt to drag the file onto the external i get a message saying

"Sorry, the operation could not be completed because an unexpected error occured. (Error code 0)"

I converted the .dmg to a .iso and i got the same error message.

Any ideas?

This file is greater then 4.7 gigs so and i cannot figure out how to burn it. This is why i ask.

Thanks very much!

If your external is formatted as Fat32, it will not take files larger than 4 GB.

i see, is there a way to change the format of an external w/o loosing all the data on it?

you need to backup your data to another drive first, then you can partition it

you can't change the filesystem without erasing it

Actualy u can! And in Windows is quite simple, just check this: Converting FAT32 to NTFS in Windows XP

After u convert the disk to NTFS ur mac won't be able to write data on it, to do so u need to install ntfs-3g for mac, check it here: NTFS-3G for Mac OS X

If u don't plan to use the disk on a windows machine, u can format it in HFS, for that I advice to backup all ur data in the disk and then use disk utility to format.

cheers