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Hello, I'm new to Sage and running into the same problem as you. I think this error happens when the object that you want to Taylor expand has a derivative that is evaluated at a specified point:

x = var('x')
u = function('u', x)
v(x) = u.diff(x)
taylor(u(x = 0), x, 0, 2) #works
taylor(v(x), x, 0, 2) #works
taylor(v(x = 0), x, 0, 2) #doesn't work

v(0) = D[0](u)(0) seems to be the problem, just like, in your case, there is a D[0](f)(0) in the Taylor expansion of g

So my guess is that issue resides in how derivatives evaluated at a fixed point are passed to Maxima..