Rails 3 problem with rake and bundler: rake aborted! Could not find RubyGem bundler (>= 0)

I'm pretty new to RoR, I have a couple of working rails apps on my computer but I must have done something wrong because now I can't create new apps. The problem is when I do this:

$ rake db:migrate

I get this:

anarres@supakewl:~/prog/rails3/myapp$ rake db:migrate
(in /home/anarres/prog/rails3/myapp)
rake aborted!
Could not find RubyGem bundler (>= 0)
/usr/local/ruby/lib/ruby/1.9.1/rubygems.rb:762:in `report_activate_error'
/usr/local/ruby/lib/ruby/1.9.1/rubygems.rb:219:in `activate'
/usr/local/ruby/lib/ruby/1.9.1/rubygems.rb:1065:in `gem'
/home/anarres/prog/rails3/myapp/config/boot.rb:2:in `<top 开发者_如何学C(required)>'
<internal:lib/rubygems/custom_require>:29:in `require'
<internal:lib/rubygems/custom_require>:29:in `require'
/home/anarres/prog/rails3/myapp/config/application.rb:1:in `<top (required)>'
<internal:lib/rubygems/custom_require>:29:in `require'
<internal:lib/rubygems/custom_require>:29:in `require'
/home/anarres/prog/rails3/myapp/Rakefile:4:in `<top (required)>'
/usr/local/ruby/lib/ruby/1.9.1/rake.rb:2373:in `load'
/usr/local/ruby/lib/ruby/1.9.1/rake.rb:2373:in `raw_load_rakefile'
/usr/local/ruby/lib/ruby/1.9.1/rake.rb:2007:in `block in load_rakefile'
/usr/local/ruby/lib/ruby/1.9.1/rake.rb:2058:in `standard_exception_handling'
/usr/local/ruby/lib/ruby/1.9.1/rake.rb:2006:in `load_rakefile'
/usr/local/ruby/lib/ruby/1.9.1/rake.rb:1991:in `run'
/usr/local/ruby/bin/rake:31:in `<main>'

I definitely have Bundler 1.0.7 installed. I installed it by doing

$ sudo gem install bundler

and I'm guessing that could be the problem because I've read in a couple of places that you're not supposed to use sudo. But if I try to do that without sudo I get a permission error. I'm running Ubuntu 10.04 and Rails 3.0.3.

Try sudo gem list just to ensure that bundler is there on your system.

Also, if you're using RVM, make sure you've installed it for the active VM - I've run into this a few times where I've switched to a different RVM, forgot to install bundler in the base gemset and fire off a task that then generated this error.