R devel - Apr 2003 - problem using mcmc

I'm using the mcmc routine from the bhat library and getting the following
error:

Error in cov(x.mon[2:m1, ] - x.mon[1:(m1 - 1), ]) :
        supply both x and y or a matrix-like x

Anyone have a clue what the problem is?

thanks

Lew Coggins