Windows 7
From Cosmoteer Wiki
As of Cosmoteer 0.15.3 32/64-bit Microsoft Windows 7 (Service Pack 1) is supported.
CLR20r3
It appears Windows 7 is prone to have a crash with a "CLR20r3" error with many programs not just Cosmoteer.
Here's a summarized page with solutions: How to Fix ‘Has Stopped Working’ CLR20r3 Event Issues Please ignore the "PC Repair Tool" ads.