XnView Software

I use XnView Version 1.97.6 (Jun 17 2010) Libformat Version 5.70.
XnView is an excellent Player for Pictures and Videos. The DiaShow in automatic-mode shows a mix of .jpg .mpg .m2ts very good.
But my AVCHD-Videos can be displayed only with Typ .m2ts .
A AVCHD-Video with Typ .mts brings a ErrorMessage: Das Format der Datei ......mts wurde nicht erkannt.
All other PlayerPrograms plays .mts-Files ok.
My System is Win7.
What can i do ???
If i change the File-Suffix from .mts to .m2ts it runs ok.
Thank you for help !

Changing filename was good idea. Otherwise, codec installation should be checked and a different direct show player (not wmp) like mentioned in topic below can verify that film is able to play on your system:
- Viewing video files within XnView: Info for FAQ wanted