I have drastically simplified my problem, see attached nb. Basically, I define f[x_]. I ask Mathematica what is f[x]? Correct result returned. I copy/paste the output of f[x]...correct plot. I ask Mathematica to plot f[x] itself...error. Why?
Try:
Plot[Evaluate@f[x], {x, 0, 2 \[Pi]}]
