gem problem on mac os x

Question

Just to make one thing clear, it's not completely a programming question but a programmer might know what's wrong:

Messed up my gem installation. If I execute "gem list" or any other gem command, I get

/Library/Ruby/Site/1.8/rubygems.rb:956:in `use_paths': undefined method `join' for #<String:0x101786480> (NoMethodError)
 from /Library/Ruby/Site/1.8/rubygems/gem_runner.rb:72:in `do_configuration'
 from /Library/Ruby/Site/1.8/rubygems/gem_runner.rb:44:in `run'
 from /usr/bin/gem:21

I reinstalled gem, the apple developer tools, ruby, googled it, ...

I need a hint!

Environment: Apple Mac OS X Snow Leopard current stable gem and Ruby 1.8.7

Answer 1

Sometime it just helps to ask the question. Solved it myself after some hours...

In .gemrc I simply had

gempath: /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8

instead of

gempath: 
- /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8

and of course the first is a String and the last is a Array (and has a join method).