NROW doesn't equal length(x)

Hi,

I am converting a data.frame to xts.  the data.frame is 4 columns and 1000 rows.  I get a message that "NROW (x) must match length(order.by)
class is data.frame, mode is list

when I run 
dim(x)   # I get 
1000     4   #which is consistent with 1000 rows and 4 columns

NROW (x)  # I get

1000  # which is the right answer  

When I run length on each of columns in x separately using the "$" I get 1000, which is the right number too.
So length on each of the columns individually gives me the right answer, but length on the data.frame gives me the number of columns instead of the number of rows, is there an explanation


thanks