Syntax error with features

Hey there!

As a beginner in programming features for OpenType I’m in a problem that a lot of you of course can solve but I’m not finding the reason of that problem.

The fact is that I’m working in a contextual alternative font with a random cycling of its characters based on a very useful tutorial of this site but when I’m trying to compile all of the features the following window appears:

I know that this is a common mistake (specially with beginners) but I think there’s not only a problem of the name of this character, but a problem with the whole class because once I’ve deleted this character to try if it’s the only with this problem, the same window appears naming another character.

I would be very greatful if someone can help me to fix that problem.

Thank you so much to everyone!

Can you send me the file by DM in this Forum?