This paper is concerned with theoretical error estimates
for a sampling formula with the sinc-Gaussian kernel.
Qian et al. have recently given
an error estimate for the class of band-limited functions
by Fourier-analytic approach.
In contrast,
we adopt in this paper a complex-analytic approach
to derive an error estimate for a wider class of functions
including unbounded functions on $\mathbf{R}$.
Part of the result of Qian et al. can be derived from ours
as an immediate corollary.
Computational results show a fairly good agreement
with our theoretical analysis.