  Data on the photoproduction of $\omega$ mesons on nuclei have been
re-analyzed in a search for in-medium modifications. The data were taken with
the Crystal Barrel(CB)/TAPS detector system at the ELSA accelerator facility in
Bonn. First results from the analysis of the data set were published by D.
Trnka et al. in Phys. Rev. Lett 94 (2005) 192303 \cite{david}, claiming a
lowering of the $\omega$ mass in the nuclear medium by 14$%$ at normal nuclear
matter density. The extracted $\omega$ line shape was found to be sensitive to
the background subtraction. For this reason a re-analysis of the same data set
has been initiated and a new method has been developed to reduce the background
and to determine the shape and absolute magnitude of the background directly
from the data. Details of the re-analysis and of the background determination
are described. The $\omega$ signal on the $Nb$ target, extracted in the
re-analysis, does not show a deviation from the corresponding line shape on a
$LH_2$ target, measured as reference. The earlier claim of an in-medium mass
shift is thus not confirmed. The sensitivity of the $\omega$ line shape to
different in-medium modification scenarios is discussed.
