Here is an example from the logfile showing the series of events from when the USB flash drive is inserted, to when the system fails during a file copy (it can happen with a single 58MB file or with 2.1MB files whether they are dragged as files or in a folder)...
8/11/12 11:27:35.382 PM fseventsd[34]: log dir: /Volumes/C_USB_2GB/.fseventsd getting new uuid: 06CDAC3D-1BEF-4510-ADA7-DC978DDE13A5
8/11/12 11:28:20.000 PM kernel[0]: USBF: 91820. 35 AppleUSBEHCI[0xffffff80198d3000]::Found a transaction which hasn't moved in 5 seconds on bus 0xfa, timing out! (Addr: 0, EP: 0)
8/11/12 11:28:26.000 PM kernel[0]: USBF: 91826. 39 AppleUSBEHCI[0xffffff80198d3000]::Found a transaction which hasn't moved in 5 seconds on bus 0xfa, timing out! (Addr: 0, EP: 0)
8/11/12 11:28:26.000 PM kernel[0]: USBF: 91826. 71 [0xffffff80199cdc00] The IOUSBFamily is having trouble enumerating a USB device that has been plugged in. It will keep retrying. (Port 4 of Hub at 0xfa100000)
8/11/12 11:28:32.000 PM kernel[0]: USBF: 91832. 44 AppleUSBEHCI[0xffffff80198d3000]::Found a transaction which hasn't moved in 5 seconds on bus 0xfa, timing out! (Addr: 0, EP: 0)
This was a drive formatted on the same MacBook Pro Mountain Lion a few minutes prior to this, so the problem is not in how this drive was formatted. It happens with other flash drives also.
Imran