Steam Client black screen

If I try to play Card Hunter using the Steam Client, I only get a black screen. Playing in the browser works fine.
This problem might be really hard to diagnose. When I look in a packet sniffer, I can see it trying to contact steam IP addresses on port 27020, but that's it.

Found the log file:

Code:

2015/07/14 22:07:08.531: === CARD HUNTER CORE PC Client ===
2015/07/14 22:07:08.531: Tue Jul 14 22:07:08 GMT-0500 2015
2015/07/14 22:07:08.531: Sandbox Type: application
2015/07/14 22:07:08.531: Version 3.34.0.10679
2015/07/14 22:07:08.546: SFS Version: 1.2.0
2015/07/14 22:07:08.546: 
2015/07/14 22:07:08.562: Create landing screen.
2015/07/14 22:07:08.562: Initializing world screen
2015/07/14 22:07:08.562: Initializing steam...
2015/07/14 22:07:08.562: *** ERROR ***
2015/07/14 22:07:08.562: Steamworks.restartAppIfNecessary(293260)
2015/07/14 22:07:08.562: Error #3500
2015/07/14 22:07:08.562: ArgumentError: Error #3500

2015/07/14 22:07:08.562: *** ERROR ***
2015/07/14 22:07:08.562: Error #3500
2015/07/14 22:07:08.562: ArgumentError: Error #3500

2015/07/14 22:07:08.578: No bootstrap configuration file.
2015/07/14 22:07:08.578: Loading configuration from ch-config.json
2015/07/14 22:07:08.656: Setting up PayPal and Google purchasing - no Steam API available
2015/07/14 22:07:22.125: Exiting application, cleaning up

Is this a Flash/AIR Security Settings problem?

 

Are you on Windows XP by any chance?

 

Yep.

 

We've only heard reports of this from XP users so far. We'll look into it. In the meantime, I guess, can you use the browser version? Thanks for your patience.