These are the .xml and .bat files I uses with Frodo on all my HTPC's, and it playback using external player only the file types specified in the rules. Music and other files playback using Frodo internal player. If all else fail, you can un-install Frodo completely and re-install it. You can give the codes below a try again....
playercorefactory.xml
<playercorefactory>
<players>
<player name="ISO_BDMV_Player" type="ExternalPlayer" audio="false" video="true">
<filename>C:\Users\Alien\AppData\Roaming\XBMC\userdata\PlayISO.bat</filename>
<args>"{1}"</args>
<hidexbmc>True</hidexbmc>
<hideconsole>true</hideconsole>
<forceontop>false</forceontop>
</player>
<player name="Disc_Player" type="ExternalPlayer" audio="false" video="true">
<filename>C:\Users\Alien\AppData\Roaming\XBMC\userdata\PlayDisc.bat</filename>
<args>"{1}"</args>
<hidexbmc>True</hidexbmc>
<hideconsole>true</hideconsole>
<forceontop>false</forceontop>
</player>
<player name="Universal_Player" type="ExternalPlayer" audio="false" video="true">
<filename>C:\Program Files\MPC-HC\mpc-hc64.exe</filename>
<args>"{1}"</args>
<hidexbmc>True</hidexbmc>
<hideconsole>true</hideconsole>
<forceontop>false</forceontop>
</player>
</players>
<rules action="prepend">
<!-- Bluray ISO/BDMV -->
<rule filetypes="iso|bdmv|mpls" player="ISO_BDMV_Player"/>
<!-- Multiple files -->
<rule filetypes="m2ts|mkv|avi|ts" player="Universal_Player"/>
<!-- Bluray Disc -->
<rule filetypes="bd|ifo" player="Disc_Player"/>
</rules>
</playercorefactory>
playiso.bat
Set file=%1
Set dummy=%file:iso=%
IF NOT %dummy% == %file% (GOTO playiso) ELSE (goto next)
:next
Set file=%1
Set dummy=%file:mpls=%
IF NOT %dummy% == %file% (GOTO plaympls) ELSE (goto playbdmv)
:playiso
"C:\Program Files (x86)\Elaborate Bytes\VirtualCloneDrive\VCDMount.exe" /d=0 %1
"C:\Program Files (x86)\ArcSoft\TotalMedia Theatre 5\uTotalMediaTheatre5.exe" J:
"C:\Program Files (x86)\Elaborate Bytes\VirtualCloneDrive\VCDMount.exe" /d=0 /u
GOTO end
:plaympls
set pth=%1
set pth=%pth:~1,-25%
"C:\Program Files (x86)\ArcSoft\TotalMedia Theatre 5\uTotalMediaTheatre5.exe" "%pth%" exit
GOTO end
:playbdmv
set pth=%1
set pth=%pth:BDMV\MovieObject.bdmv=%
set pth=%pth:BDMV\index.bdmv=%
"C:\Program Files (x86)\ArcSoft\TotalMedia Theatre 5\uTotalMediaTheatre5.exe" %pth% exit
GOTO end
:end
exit
playdisc.bat
@
echo off
"C:\Program Files (x86)\ArcSoft\TotalMedia Theatre 5\uTotalMediaTheatre5.exe" E: