Oil pressure gauge is reading max pressure and stays there. Not sure if the sending unit would be bad or if there is actually a problem causing high oil pressure

Update from Sep 13, 2009: replaced the oil pressure sending unit and it fixed the problem, the guage now reads accurately

My oil gauge started reading max oil pressure then would drop to 0. Now it only reads no oil pressure at all. Oil Change place says the dip stick show normal. I haven't noticed any difference in the engine since first noticed problem.