Troubleintalling wxruby with ruby gems 1.3.5

I’ve updated to Ruby Gems version 1.3.5. When I then run the command

‘gem install wxruby’

I get an error message that says

ERROR: While executing gem … (TypeError)
incompatible marshal file format (can’t be read)
format version 4.8 required; 23.71 given

I’m using Ruby 1.9.1 (p. 378).

Other gems have installed fine. Any ideas?