When you repeat parameters on the command line mongod errors as follows
c:\mongo\mongodb-win32-x86_64-2008plus-2.5.2\bin>..\..\mongodb-win32-x86_64-2008
plus-2013-09-13\bin\mongod.exe --port 27017 --port 27017 --port 27017
Error parsing command line: BadValue Error parsing command line: multiple occurrences
use --help for help
Error parsing command line: BadValue Error parsing command line: multiple occurrences
Specifying which options are repeated will greatly help. Also note the message is printed twice.