I've had this long-running problem, that while trying to read one of my unpublished stories, after a certain point all links lead to this one error message.
I'll be honest- I got no idea what's going on.
The thing is- once I get to the certain point, there's four links, three don't change any variables and one of them does a very simple -1 variable for a variable with more than 1 on it up to that point, yet all options lead to an error message.
And it's an unpublished game of mine I'm working on, I don't have it as a preview on my account(yet, at least).
There's not even all that much to the game yet, very minimal variables to be messing anything up with.
Are you using on-page coding on the page just before the error? Sometimes extra characters from HTML (which is hidden in rich text) gets between those percentage signs and messes with variable handling which is then realized on the following page. If you do, try editing the HTML out via the source; or cut the passage and either paste it into notepad (or some other plain text editor) and back, or paste it right back in as plain text (Ctrl-Shift-V).
Oh fuck this might have been it. I like to customize a lot of my text, and after getting rid of all that and putting it back in as just plain text, it started working again. Thanks a lot dude!
(Although now I feel really stupid for not realizing sooner-)