Hey Shargass,

So I was pretty bored today and decided to take a crack at this on my own. I figured out the cause and the solution, here are the details for you:

Cause: The issue is caused by Overwolf's GameList xml file not accounting for a 64bit hearthstone install. Specifically the following chunk of code:

<GameInfo>
  <ID>98981</ID>
  <GameTitle>Hearthstone: Heroes of Warcraft</GameTitle>
  <DisplayName>Hearthstone</DisplayName>
  <ProcessNames>
      <string>Hearthstone.exe</string>
  </ProcessNames>
  <LuancherNames>
      <string>Hearthstone Beta Launcher.exe</string>
  </LuancherNames>
  <GameRenderers>D3D9</GameRenderers>
  <InjectionDecision>Supported</InjectionDecision>
  <LauncherDirectoryRegistryKey>HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Hearthstone\InstallLocation</LauncherDirectoryRegistryKey>
  <GameGenres>Puzzle_Cards</GameGenres>
  <XPSupport>NotSupported</XPSupport>
  <Client_GameControlMode>MixedAlwaysAvailable</Client_GameControlMode>
  <RestoreRT>true</RestoreRT>
  <Launchable>True</Launchable>
  <FixRCEx>True</FixRCEx>
  <UseMCH>6;10</UseMCH>
  <FIGVTH>True</FIGVTH>
  <EnableTXR>True</EnableTXR>
  <KeepInGameOnLostFocus>True</KeepInGameOnLostFocus>
</GameInfo>
<GameInfo>
  <ID>98982</ID>
  <GameTitle>Hearthstone: Heroes of Warcraft</GameTitle>
  <DisplayName>Hearthstone</DisplayName>
  <LuancherNames>
      <string>Hearthstone.exe</string>
  </LuancherNames>
  <GameRenderers>D3D9</GameRenderers>
  <InjectionDecision>Supported</InjectionDecision>
  <LauncherDirectoryRegistryKey>HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Hearthstone\InstallLocation</LauncherDirectoryRegistryKey>
  <XPSupport>NotSupported</XPSupport>
  <Client_GameControlMode>MixedAlwaysAvailable</Client_GameControlMode>
  <RestoreRT>true</RestoreRT>
  <Launchable>True</Launchable>
  <FixRCEx>True</FixRCEx>
  <UseMCH>6;10</UseMCH>
  <FIGVTH>True</FIGVTH>
  <EnableTXR>True</EnableTXR>
  <KeepInGameOnLostFocus>True</KeepInGameOnLostFocus>
</GameInfo>            

Now you will notice the following line present in each of these two GameInfo objects:

  <LauncherDirectoryRegistryKey>HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Hearthstone\InstallLocation</LauncherDirectoryRegistryKey>

This will work just fine if you have a 32bit version of hearthstone installed. But for a 64bit install this key does not exist. Instead the key it should be checking to find the games install directory is:

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall\Hearthstone\InstallLocation

So in order to fix the issue simply replace