  Given a $(2,d)$-Gaussian field \[ Z=\big\{ Z(t,s)= X^{H_1}_t
-\tilde{X}^{H_2}_s, s,t \ge 0\big\}, \] where $X^{H_1}$ and $\tilde{X}^{H_2}$
are independent $d$-dimensional centered Gaussian processes satisfying certain
properties, we will give the necessary condition for existence of derivatives
of the local time of $Z$.
