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Expand the traceback. You'll see that "assume ... may help" (or words to that effect). Indeed:

from sage.calculus.calculus import symbolic_sum
n = var('n')
var('x'); assume(x==0)
print 1/(1 + symbolic_sum(factorial(n) * x^n, n, 1, oo))

gives the answer you got in 7.4:

1/(x*hypergeometric((1, 2), (), x) + 1)

However, if we assume (x>0) or assume (x<0), we get "Sum divergent".

Expand the traceback. You'll see that "assume ... may help" (or words to that effect). Indeed:

from sage.calculus.calculus import symbolic_sum
n = var('n')
var('x'); assume(x==0)
print 1/(1 + symbolic_sum(factorial(n) * x^n, n, 1, oo))

gives the answer you got in 7.4:

1/(x*hypergeometric((1, 2), (), x) + 1)

However, if we assume (x>0) or assume (x<0), we get "Sum divergent".