Do you have any other versions of FFXI installed be it retail or another private server? If so, your registry keys may be out of whack. I would have thought that the nasomi install would have updated the keys for you, but maybe it didnt if you did not run it as admin or something. To fix the keys yourself, copy and past this into a notepad, update paths to NasomiXI and save as a .bat file. Run it as admin.

regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\FINAL FANTASY XI\FFXi.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\FINAL FANTASY XI\FFXiMain.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\FINAL FANTASY XI\FFXiResource.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\FINAL FANTASY XI\FFXiVersions.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\PlayOnlineViewer\polhook.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\PlayOnlineViewer\unicows.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\PlayOnlineViewer\patchfiles\PlayOnlineViewer\viewer\com\app.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\PlayOnlineViewer\patchfiles\PlayOnlineViewer\viewer\com\polcore.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\PlayOnlineViewer\polcfg\sysinfo.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\PlayOnlineViewer\util\unicows.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\PlayOnlineViewer\viewer\ax\MSVCR71.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\PlayOnlineViewer\viewer\ax\polmvf.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\PlayOnlineViewer\viewer\ax\polmvfINT.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\PlayOnlineViewer\viewer\com\app.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\PlayOnlineViewer\viewer\com\polcore.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\PlayOnlineViewer\viewer\contents\PolContents.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\PlayOnlineViewer\viewer\contents\polcontentsINT.dll" /s
regsvr32 "~path to NasomiXI~\NasomiXI\SquareEnix\TetraMaster\TM.dll" /s
@PAUSE

where ~path to NasomiXI~ in my case is G:\Games\

Note: Once thats ran you will have an issue launching other private servers or retail in which case you can run this to set it back like above:

regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\FINAL FANTASY XI\FFXi.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\FINAL FANTASY XI\FFXiMain.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\FINAL FANTASY XI\FFXiResource.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\FINAL FANTASY XI\FFXiVersions.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\PlayOnlineViewer\polhook.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\PlayOnlineViewer\unicows.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\PlayOnlineViewer\patchfiles\PlayOnlineViewer\viewer\com\app.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\PlayOnlineViewer\patchfiles\PlayOnlineViewer\viewer\com\polcore.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\PlayOnlineViewer\polcfg\sysinfo.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\PlayOnlineViewer\util\unicows.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\PlayOnlineViewer\viewer\ax\MSVCR71.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\PlayOnlineViewer\viewer\ax\polmvf.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\PlayOnlineViewer\viewer\ax\polmvfINT.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\PlayOnlineViewer\viewer\com\app.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\PlayOnlineViewer\viewer\com\polcore.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\PlayOnlineViewer\viewer\contents\PolContents.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\PlayOnlineViewer\viewer\contents\polcontentsINT.dll" /s
regsvr32 "~path to Playonline~\PlayOnline\SquareEnix\TetraMaster\TM.dll" /s
@Pause

where ~path to Playonline~ in my case was E:\Program Files (x86)