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This is a typical error message from Sage via Maxima.

But maybe I need an update from you. I get

sage: N, n, f  = var('N, n, f')
sage:  assume(N>0)
sage:  sum(binomial(N, n)*f^n*(1-f)^(N-n), n, (N+1)/2, N)
sum((-f + 1)^(N - n)*f^n*binomial(N, n), n, 1/2*N + 1/2, N)