No rmagick after update

[macaco]

[Note: parts of this message were removed to make it a legal post.]

Hi list.

Some days ago I've updated my kubuntu and my ruby server just stop, I
decided to run a "gem update" and everything seem to be ok.

but i get to this line of code:

send_data(g.paint(XMAX*MULT,YMAX*MULT,MULT).to_blob, {:type => 'image/jpeg',
:disposition => 'inline'})

which used to work before, and now it's throwing an error:

no decode delegate for this image format `'
app/controllers/generate_controller.rb:37:in `to_blob'


I assume it's a matter of updating, so I run 'gem update rmagick' and it
says:
Successfully installed rmagick-2.5.0

Stop the server, run again, and I have the same error.

Any help?