  We test the "reprocessing paradigm" of the optical -- UV AGN variability by
detailed modeling of the correlated X-ray -- optical (3590 and 5510 Angstrem)
variability of the recent multiwavelength campaign of NGC 3516. We produce
model optical light curves by convolving the observed X-ray flux with the
response function of an infinite, thin accretion disk, illuminated by a
point-like X-ray source at a given height above the compact object (the
lamp-post model) and compare their properties to those observed. Special
attention is given to the correct computation of the X-ray albedo of the disk.
We further compute the X-ray reflection response at two energies (E = 1 and 20
keV) and argue for the possibility of hard lags in their cross spectra. We also
compute the continuum Optical -- UV and the X-ray reflection spectra as well as
the Fe K-alpha fluorescent line profiles which we also compare to observations.
Despite the large (~50 percent) amplitude excursions of the X-ray flux, the
model optical light curves exhibit variability amplitudes of 3 -- 4 percent,
not unlike those observed. However, the model CCF between the X-ray and the
model optical variations show clear lags of 0.1 and 0.25 days for black hole
masses M = 10^7 and 10^8 Solar masses, respectively, not apparent in the data.
The synchrony of X-ray - optical variations points toward the BH mass < 10^7
Solar masses, whereas the X-ray spectra prefer BH mass > 10^8. Our conclusion
is that the combination of the observed optical/UV/X-ray spectral and timing
observations are inconsistent with the lamp-post model geometry for NGC 3516.
