`instance_method': {:metaclass=>:singleton_class} is not a symbol (TypeError) *RESOLVED*

I got this error today when trying to run a Sinatra web application. Not sure what the root of the problem is, but I found a workaround:

sudo gem1.9.1 install activesupport --version 2.3.5

$ sudo gem uninstall activesupport

Select gem to uninstall:
 1. activesupport-2.3.5
 2. activesupport-2.3.8
 3. All versions
> 2   

For reference, the full error:

/var/lib/gems/1.9.1/gems/deprecated-2.0.1/lib/deprecated.rb:176:in `instance_method': {:metaclass=>:singleton_class} is not a symbol (TypeError)
    from /var/lib/gems/1.9.1/gems/deprecated-2.0.1/lib/deprecated.rb:176:in `block in <top (required)>'
    from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/core_ext/object/metaclass.rb:13:in `<class:Object>'
    from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/core_ext/object/metaclass.rb:3:in `<top (required)>'
    from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/core_ext/object.rb:5:in `require'
    from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/core_ext/object.rb:5:in `<top (required)>'
    from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/core_ext.rb:8:in `require'
    from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/core_ext.rb:8:in `block in <top (required)>'
    from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/core_ext.rb:8:in `each'
    from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/core_ext.rb:8:in `<top (required)>'
    from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support.rb:56:in `require'
    from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support.rb:56:in `<top (required)>'
    from /var/lib/gems/1.9.1/gems/mail-2.2.1/lib/mail.rb:6:in `require'
    from /var/lib/gems/1.9.1/gems/mail-2.2.1/lib/mail.rb:6:in `<module:Mail>'
    from /var/lib/gems/1.9.1/gems/mail-2.2.1/lib/mail.rb:2:in `<top (required)>'
    from /var/lib/gems/1.9.1/gems/pony-1.0/lib/pony.rb:2:in `require'
    from /var/lib/gems/1.9.1/gems/pony-1.0/lib/pony.rb:2:in `<top (required)>'
    from /home/albertlash/svxbox/lib/svxbox/ponyboy.rb:6:in `require'
    from /home/albertlash/svxbox/lib/svxbox/ponyboy.rb:6:in `<top (required)>'
    from /home/albertlash/svxbox/lib/svxbox.rb:8:in `require'
    from /home/albertlash/svxbox/lib/svxbox.rb:8:in `<top (required)>'
    from /home/albertlash/yodnsconf/yodnsconf.rb:45:in `require'
    from /home/albertlash/yodnsconf/yodnsconf.rb:45:in `<top (required)>'
    from config.ru:11:in `require'
    from config.ru:11:in `block in <main>'
    from /var/lib/gems/1.9.1/gems/rack-1.1.0/lib/rack/builder.rb:46:in `instance_eval'
    from /var/lib/gems/1.9.1/gems/rack-1.1.0/lib/rack/builder.rb:46:in `initialize'
    from config.ru:1:in `new'
    from config.ru:1:in `<main>'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:46:in `eval'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:46:in `block in builder'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:816:in `call'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:816:in `build_app!'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:673:in `init_worker_process'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:688:in `worker_loop'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:605:in `block (2 levels) in spawn_missing_workers'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:602:in `fork'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:602:in `block in spawn_missing_workers'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:598:in `each'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:598:in `spawn_missing_workers'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:612:in `maintain_worker_count'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:408:in `block in join'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:396:in `loop'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:396:in `join'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/lib/unicorn.rb:28:in `run'
    from /var/lib/gems/1.9.1/gems/unicorn-0.99.0/bin/unicorn:126:in `<top (required)>'
    from /var/lib/gems/1.9.1/bin/unicorn:19:in `load'
    from /var/lib/gems/1.9.1/bin/unicorn:19:in `<main>'
I, [2010-05-28T04:48:24.242011 #28838]  INFO -- : reaped #<Process::Status: pid 28848 exit 1> worker=0
I, [2010-05-28T04:48:24.242246 #28838]  INFO -- : master complete