I've battled with this for some time and then changed the Wine Version and also added a library and it seems to be working (installing) now.
So my wowmop.pol file like looks this (I am using the Europe version of the installer):
#!/bin/bash
if [ "$PLAYONLINUX" = "" ]
then
exit 0
fi
source "$PLAYONLINUX/lib/sources"
TITLE="World of Warcraft : Mists of Pandaria"
cfg_check
POL_SetupWindow_Init
POL_SetupWindow_presentation "World of Warcraft : Mists of Pandaria" "Activision / Blizzard Entertainment" "http://www.worldofwarcraft.com" "Silverman" "WorldOfWarcraft"
POL_Wine_SelectPrefix "WorldOfWarcraft"
POL_Wine_PrefixCreate "1.5.21"
POL_Wine_OverrideDLL "builtin" "dnsapi"
POL_System_TmpCreate "WorldOfWarcaft"
POL_SetupWindow_InstallMethod "LOCAL"
cd "$HOME"
POL_SetupWindow_browse "Please select the installation file to run." "World-of-Warcraft-Setup-enGB.exe"
POL_SetupWindow_wait "Installing World of Warcraft : Mists of Pandaria." "World of Warcraft : Mists of Pandaria"
POL_Wine start /unix "$APP_ANSWER"
POL_System_TmpDelete
POL_Wine_WaitExit "$TITLE"
POL_Shortcut "World of Warcraft Launcher.exe" "" "World of Warcraft : Mists of Pandaria Launcher"
POL_Shortcut "Wow.exe" "$TITLE"
POL_SetupWindow_Close
exit
Now you can open PlayOnLinux
From the menus go to: Tools -> Run as local script
Select the wowmop.pol file and follow the instructions