I've used the latest official version of ruby(
1.9.2p0) while developing this binding. I have no idea if it works on any older version. It worked compiling for me though, so that might be the issue.
Also the rake file is maintained by trickster, I have no idea of how rake works so we'll see if he responds to it.
EDIT: Just tried it and it worked like a charm
I'm guessing on that you using the old 1.8.x ruby is the problem because we both have the same rake version.
The problem also seems to be syntax errors, which would pretty much confirm it, since there are some new syntax tricks to ruby-1.9.x
I could see if Trickster is willing to make the file compatible with 1.8.x but I'm not sure if it would still compile.
And a final note: You are allowed to create new threads on the forum for anything ruby-ish
Though I'm really glad to see that people are starting to use rbSFML ^^