Error producing brm code

gistfile1.txt

brms.mod.attesa.prior <- brm(bf(Attesa ~ log(N.prest) + (log(N.prest)|Context), shape ~ log(N.prest) + (log(N.prest)|Context), family = Gamma('log')), data = TdA, prior = c(
    set_prior('normal(0, 2.5)', class = 'Intercept'),
    set_prior("cauchy(0, 2.5)", class = 'b'),
    set_prior("normal(0, 1.5)", class = 'sd',  group = 'Context'),
    set_prior("normal(0, 1.5)", class = 'sd'),
    set_prior("student_t(3, 0, 2.5)", class = 'sd', dpar = 'shape'),
    set_prior("student_t(3, 0, 2.5)", class = 'sd', group = 'Context', dpar = 'shape')
), init_r = 0.1, cores = 8, chains = 8, iter = 8000, warmup = 2000, control = list(max_treedepth = 15, adapt_delta = .90))

Error in stan_base_prior(prior) : length(base_prior) == 1L is not TRUE
In addition: Warning message:
Rows containing NAs were excluded from the model.