what did I do wrong with evapo-rust?

[aggressive male]

Usually when I soak something in evapo-rust a couple of weeks it works well, I spray it off dry it and paint it. This time I wanted to be real sure it was rust free so I left it in a couple of months. Now I have this thick yellow cake like stuff all over it. I'm having a hard time spraying it off. what happend? And how do I get this cakey yellow stuff off?