Rubygems: can't install rails (not in gzip format)

I want to install rails to use it with aptana studio 3. After hiting gem install rails following error is being thrown:

ERROR:  开发者_C百科While executing gem ... (Zlib::GzipFile::Error)
    not in gzip format

I installed ruby 1.9.2 and and rubygems 1.8.9 seperately (after that I read about ruby 1.9.1+ including gem support already).

My gem source is: http://rubygems.org/

I have searched for solutions for quite some time. But can't find the issue.

Your help is appreciated :-)

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EDIT1:

All right. After using the RailsInstaller I can find Rails in my gem-folder. When I try to open a project in Aptana I get the following Error:

sh.exe":C:/Projects/railsinstaller/Stage/Ruby1.9.2/bin/ruby.exe: bad interpreter: No such file or directory

found simialar issue here and here. but didn't help in my case.

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EDIT2:

I started a new topic since I solved this issue indirectly and a new one occured. To follow my further steps go here

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I have found a solution but not a direct one:

http://railsinstaller.org/ <-- here you can find an install-package that istalls all you need...

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I used RailsInstaller for Windows but I still had that Aptana error, which I solved by simply calling:

$ gem update

than, on my project

$ bundle update

My error was:

sh: /c/RailsInstaller/Ruby1.9.2/bin/rails: C:/Projects/railsinstaller/Stage/Ruby1.9.2/bin/ruby.exe: bad interpreter: No such file or directory

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gem update will work. This is because most of the bat files in bin directory refers to wrong railsInstaller path.