No, there's no such thing as "Crafting Fatigue," that makes you fail synth attempts if you've been crafting too much.

Cid is right. Brass Dishes require Guild support. Here's a link to Yellow Gremlin, showing that you need Guild support. Also, when you start the synth, and you get the message like "This synth would benefit from a higher level of support," that means you should get a higher level of support to do the synth.

That could be the problem. Or it could just be a streak of bad luck with the random number generator.