Ran into this error today:

Incompatible library version: nokogiri.bundle requires version 8.0.0 or later, but libiconv.2.dylib provides version 7.0.0

Fortunately, uninstalling the nokogiri gem and reinstalling it solved the problem. Easy fix, thanks to this StackOverflow question (and answer).

I think it may have been caused by the same trigger, in that I recently migrated from MacPorts to homebrew on this system after having repeated conflicts between Lion’s built in PostgreSQL and the port install.