Within a Two-Higgs-Doublet Model (2HDM) a search for a light Higgs
boson in the mass range of 4--12 GeV has been performed in the Yukawa
process $\rm e^+e^-\rightarrow b\bar{b} A/h\rightarrow b\bar{b}\tau^+\tau^-$, 
using
the data collected by the OPAL detector at LEP between 1992 and 1995
in $\rm e^+e^-$ collisions at about 91 GeV centre-of-mass energy.  A
likelihood selection is applied to separate background and signal.
The number of observed events is in good agreement with the expected
background. Within a CP-conserving 2HDM type II model the
cross-section for Yukawa production depends on $\xi^{\rm A}_d=|\tan\beta|$ and
$\xi^{\rm h}_d=|\sin\alpha/\cos\beta|$ for the production of the CP-odd A
and the CP-even h, respectively, where $\tan\beta$ is the ratio of
the vacuum expectation values of the Higgs doublets and $\alpha$ is
the mixing angle between the neutral CP-even Higgs bosons. From our
data 95\% C.L.  upper limits are derived for $\xi^{\rm A}_d$ within the range
of 8.5 to 13.6 and for $\xi^{\rm h}_d$ between 8.2 to 13.7, depending on the
mass of the Higgs boson, assuming a branching fraction into $\tau^+\tau^-$ of
100\%. An interpretation of the limits within a 2HDM type II model
with Standard Model particle content is given.  These results impose
constraints on several models that have been proposed to explain
the recent BNL measurement of the muon anomalous magnetic moment.