Ruby interpreter 1.8.7.0 [i386-mingw32] keeps failing

Question

I have had this problem for a while, but now it is getting so bad that every 2-3 pageloads my local server is failing.

activesupport-2.3.5/lib/active_support/core_ext/module/introspection.rb:73: [BUG] gc_sweep(): unknown data type 0x0(0x950f868)
ruby 1.8.7 (2010-01-10 patchlevel 249) [i386-mingw32]

This application has requested the RunTime to terminate it in an unusual way. Please contact the application's support team for more information.

Introspection.rb:73:

73    constants.select do |const|
74      !inherited.key?(const) || inherited[const].object_id != const_get(const).object_id
75    end

I'm running Vista 64-bit (but the site will probably be served on Linux eventually).

What's causing this? I'm not experienced with these kinds of issues so a specific reply would be most helpful. Thank you!