The operation can’t be completed because the item "Filename.CR2" is in use.....

I tried a search for this issue, but it didn't turn up anything....I am a photographer and deal with a large amount of large files that I transfer from Compact Flash cards onto an ioMega StorCenter ix2 RAID external HD via a 27" iMac. The file sizes I am dealing with are around 20mb and I usually transfer between 400 and 1000 at a time. Recently, when I drag the files from the CF card to a folder within the ix2, it will begin copying, then stop with the error "The operation can’t be completed because the item “Filename.CR2” is in use. When I click "OK" it will then stop the transfer. It is VERY frustrating. This seems to have started when I purchased a new camera with larger sized image files. Any ideas? Any and all replies would be greatly appreciated!

Could be the limit on read /write speed of your drive or connection type.