I am not sure what do you mean by "the dot notation". Does it mean the remote directory separator is dot?
However it seems you are not using the latest version. Can you please try it with the latest trial version?
Also please note that the
XCopy option is recursive and traverses all subdirectories. If the files are all in the same ABC directory (and not in subdirectories), the best way to download these files is:
ftp.Download("N10.AB10000.ABC.20.*", @"c:\test", TraversalMode.MatchFilesShallow, TransferMethod.Copy, ActionOnExistingFiles.OverwriteAll);