A few people answered correctly to my little challenge, but not everyone.

At first sight, the rules look pretty favorable to the player: half of the time, I lose my money, but the other half, I get back at least as much as I bet.

Or do I?

Well, no. If you look at the rules carefully, you realize that what you are getting back if the roll is over 50 is not as obvious as it looks. Take the 66-75 range: you get 1.5 times your money, but you need to remember that part of this is the original bet. So if you bet $1, rolling between 66 and 75 will only make you richer by $0.5 and not $1.5. And the same applies to the other rolls.

Your gain expectation therefore is:

-1*0.50 + 0.5*0.10 + 1*0.24 + 2*0.01 = -0.19

For every dollar you bet, you will lose 19 cents.

Here is a simulation in Ruby:

fortune = 0
max = 1000000
for i in 1..max do
n = (rand * 100).round
if (n < 50) then fortune = fortune - 1
elsif (n >= 50 && n <= 64) then fortune = fortune + 0
elsif (n >= 65 && n <= 75) then fortune = fortune + 0.5
elsif (n >= 76 && n <= 99) then fortune = fortune + 1
elsif (n == 100) then fortune = fortune + 2
else puts "#{i}: n:#{n}"
end
end
puts fortune

and the output:

$ ruby ~/t/game.rb
-184887.0

The mistake that a few commenters made (and which I made as well initially) was to have a few extra "ones" in their gain calculation.