If I double-click on a music file (like an MP3) in Windows Explorer then Media Center launches with a message that says "Please select file(s) to play".
I have this same problem.
Media Center Registered 9.1.299 -- C:\Program Files\J River\Media Center\
Microsoft Windows Me
Intel Celeron 368 MHz MMX / Memory: Total - 261 MB, Free - 86 MB
Resource Info: System - 46 %, GDI - 60 %, User - 46 %
Internet Explorer: 6.0.2800.1106 / ComCtl32.dll: 5.81 / Shlwapi.dll: 6.00.2800.1226 / Shell32.dll: 5.50.4134.100 / wnaspi32.dll: 4.71 (0002) , ASPI for Win32 (95/NT) DLL, Copyright © 1989-2002 Adaptec, Inc. / Aspi32.sys: N/A
Ripping / Drive D: Copy mode:Normal CD Type:Auto Read speed:Max
Drive E: Copy mode:Normal CD Type:Auto Read speed:Max
Digital playback: Yes / Use YADB: Yes / Get cover art: No / Calc replay gain: Yes / Copy volume: 32767
Eject after ripping: No / Play sound after ripping: No
Burning / Drive E: HP CD-Writer+ 8200f Addr: 1:0:0 Speed:4 MaxSpeed:4 BurnProof:No