Moving iPhoto Library on External Drive

Hi

I have been trying, unsuccessfully, to move my iPhoto library. At present it is located on an external hard drive. Problem is I am now running out of space on that drive and have been trying to move the library to another external hard drive.

I have tried "copy & paste and drop & drag". I keep getting this message in a pop up window:

"You can’t copy “iPhoto Library” because it has the same name as another item on the destination volume, and that volume doesn’t distinguish between upper- and lowercase letters in filenames."

Please help

I think the message is very self-explanatory. It's telling you that your "another external hard drive" either needs to not have a copy of iPhoto Library on it, or you need to reformat the volume so that it's case-sensitive.