  We have used Hubble/WFC3 and the G141 grism to measure the secondary eclipse
of the transiting very hot Jupiter CoRoT-2b in the 1.1-1.7$\mu$m spectral
region. We find an eclipse depth averaged over this band equal to
$395^{+69}_{-45}$ parts per million, equivalent to a blackbody temperature of
$1788\pm18$K. We study and characterize several WFC3 instrumental effects,
especially the "hook" phenomenon described by Deming et al. (2013). We use data
from several transiting exoplanet systems to find a quantitative relation
between the amplitude of the hook and the exposure level of a given pixel.
Although the uncertainties in this relation are too large to allow us to
develop an empirical correction for our data, our study provides a useful guide
for optimizing exposure levels in future WFC3 observations. We derive the
planet's spectrum using a differential method. The planet-to-star contrast
increases to longer wavelength within the WFC3 bandpass, but without water
absorption or emission to a $3\sigma$ limit of 85 ppm. The slope of the WFC3
spectrum is significantly less than the slope of the best-fit blackbody. We
compare all existing eclipse data for this planet to a blackbody spectrum, and
to spectra from both solar abundance and carbon-rich (C/O=1) models. A
blackbody spectrum is an acceptable fit to the full dataset. Extra continuous
opacity due to clouds or haze, and flattened temperature profiles, are strong
candidates to produce quasi-blackbody spectra, and to account for the amplitude
of the optical eclipses. Our results show ambiguous evidence for a temperature
inversion in this planet.
