The dynamics of a fragile glass-farmer (diglycidyl ether of bisphenol-A) has been studied by wideband dielectric spectroscopy down to the temperature-induced and the pressure-induced glass transition. A full check of the temperature and pressure dependence of the structural relaxation time, predicted within an extended free volume model by the generalised Cohen-Grest function, is reported. From our investigation it is evident that this function suitably describes the structural relaxation time at ambient pressure, but on the other hand, it strikingly fails in describing the isothermal data under variable pressure.