heatmap.2 in gplots package

Hello all,

I am using the heatmap.2 function in the gplots package. I want to supress the
reordering of the columns of the data matrix i pass to the function. I used
the statement,

heatmap.2(z,Colv=FALSE,dendrogram="row",col=redgreen(75))

where z, is the matrix of data. The output i want should have the rows
reordered along with the dendrogram and the columns should be in the original
order without any dendrogram. For the above statement i am getting an error:

Error in image.default(1:nc, 1:nr, x, xlim = 0.5 + c(0, nc), ylim = 0.5 +  :
        dimensions of z are not length(x)(+1) times length(y)(+1)

I also tried using ,
heatmap.2(z,Colv=NULL,dendrogram="row",col=redgreen(75))
for which i am getting the output, but the columns are reordered. How can this
be done for the way in which i want the map to appear?