TS search for adsorbed reactant and desorbed product

Hi All,
I have an issue while doing TS search calculation for a particular system, where the reactant is adsorbed over a surface and the product desorbed from the surface. The Barrier value that it calculates is unexpectedly high. Is this due to some artifact when one has reactant adsorbed and product desorbed? Is there any way to resolve this?
Thanks,
Regds,
Aarthi