I believe there's a bug in the way buildr reads POMs on Ruby 1.9 (or compatible) rubies. It assumes that the POM's XML can be read in the ruby's default external encoding. On my machine with ruby 1.9.3-p194 that encoding is UTF-8 (so the commons-exec POM is read fine), but in your environment the default encoding seems to be US-ASCII (causing your problem). You could confirm this by putting puts Encoding.default_external.inspect
somewhere in your buildfile and seeing what it gives you.
So long as all the files you want buildr to read are UTF-8 (or UTF-8 compatible, like ASCII), you should be able to work around this problem by putting the following at the top of your buildfile:
Encoding.default_external = 'UTF-8'
See if that works. If it does, I encourage you to file a bug against buildr so that they know about the problem. (In general, you do not want to be messing with Encoding.default_external
since it's a global setting.)