The game crashed on opponent's turn. I played against a Shapeshifter, the duel was initiated from a Spectral Arena random event. See screenshot as well.

Here is the error information Windows gathered:
Problem signature:
Problem Event Name: APPCRASH
Application Name: Shandalar.exe
Application Version: 6.1.0.0
Application Timestamp: 3517e16d
Fault Module Name: shandalar.dll
Fault Module Version: 0.0.0.0
Fault Module Timestamp: 55c021ae
Exception Code: c0000005
Exception Offset: 001c1740
OS Version: 6.1.7601.2.1.0.256.1
Locale ID: 1031
Additional Information 1: 0a9e
Additional Information 2: 0a9e372d3b4ad19135b953a78882e789
Additional Information 3: 0a9e
Additional Information 4: 0a9e372d3b4ad19135b953a78882e789