/usr/lib/ruby/gems/1.8/gems/rmagick-1.15.10/lib/RMagick.so: libMagick.so.9: cannot open shared object file: No such file or directory - /usr/lib/ruby/gems/1.8/gems/rmagick-1.15.10/lib/RMagick.so (LoadError)

This problem happenned after I updated Ubuntu to 8.0.4 and Ruby to ruby 1.8.6 (2007-09-24 patchlevel 111) [i486-linux].

Very simple solution: update to the latest version of rmagick!

sudo gem update rmagick