When gem is installed I get something like:

Successfully installed oniguruma-1.1.0
Installing ri documentation for oniguruma-1.1.0...

No definition for oregexp_initialize
Installing RDoc documentation for oniguruma-1.1.0...

No definition for oregexp_initialize


Then when I try to use ultraviolet for example I get this:

/usr/lib/ruby/1.8/rubygems/custom_require.rb:27:in `gem_original_require': no such file to load -- oregexp (LoadError)
        from /usr/lib/ruby/1.8/rubygems/custom_require.rb:27:in `require'
        from /var/lib/gems/1.8/gems/oniguruma-1.1.0/lib/oniguruma.rb:1
        from /usr/lib/ruby/1.8/rubygems/custom_require.rb:33:in `gem_original_require'
        from /usr/lib/ruby/1.8/rubygems/custom_require.rb:33:in `require'
        from /var/lib/gems/1.8/gems/textpow-0.10.0/lib/textpow.rb:2
        from /usr/lib/ruby/1.8/rubygems/custom_require.rb:33:in `gem_original_require'
        from /usr/lib/ruby/1.8/rubygems/custom_require.rb:33:in `require'
        from /var/lib/gems/1.8/gems/ultraviolet-0.10.1/bin/../lib/uv.rb:2
        from /usr/lib/ruby/1.8/rubygems/custom_require.rb:33:in `gem_original_require'
        from /usr/lib/ruby/1.8/rubygems/custom_require.rb:33:in `require'
        from /var/lib/gems/1.8/gems/ultraviolet-0.10.1/bin/uv:8
        from /var/lib/gems/1.8/bin/uv:18:in `load'
        from /var/lib/gems/1.8/bin/uv:18


I have no idea how to fix it - can you help me with this?