paramErr = -50, /*error in user parameter list*/
Not too helpful by itself, but can mean an unacceptable character in a filename like...
? / \\ < > " | > *
when copying to a FAT32 formatted drive or using SMB for file transfer. Can also be a Permissions problem, usually on the receiving end, & in the old days could happen if a file had forks...
http://support.apple.com/kb/TA20831