I get following warning when I try the example given on the homepage:

E:/Ruby/lib/ruby/gems/1.8/gems/gga4r-0.9.0/lib/gga4r/gga4r_main.rb:93: warning: instance variable @logger
not initialized
E:/Ruby/lib/ruby/gems/1.8/gems/gga4r-0.9.0/lib/gga4r/gga4r_main.rb:94: warning: instance variable @logger
not initialized

I fixed it with replacing

line 24> @logger = prop[:logger] if prop[:logger]

through

line 24> @logger = prop[:logger] || nil

Hope that helps.

Dominik