As a workaround, use "img.fuzz= options.fuzz * QuantumRange / 100.0
Otherwise see this error message:
Input: demo.mov (00:00:04.29, 5.8M)
Output: 'demo2.gif' (128K)
/var/lib/gems/1.9.1/gems/screengif-0.0.1/lib/screengif.rb:92:in `fuzz=': no implicit conversion to float from string (TypeError)
from /var/lib/gems/1.9.1/gems/screengif-0.0.1/lib/screengif.rb:92:in `block in start'
from (eval):2:in `each'
from (eval):2:in `each'
from /var/lib/gems/1.9.1/gems/screengif-0.0.1/lib/screengif.rb:83:in `each_with_index'
from /var/lib/gems/1.9.1/gems/screengif-0.0.1/lib/screengif.rb:83:in `start'
from /var/lib/gems/1.9.1/gems/screengif-0.0.1/bin/screengif:10:in `<top (required)>'
from /usr/local/bin/screengif:23:in `load'
from /usr/local/bin/screengif:23:in `<main>'