Troubles on retrieving rownames

Hi guys, I am using the blp() function from RBloomberg package which  
returns
a matrix of prices with the columns corresponding to the security  
name and
the columns to the date. When I have a look at the matrix I can see  
the
rownames (dates) on the left of the prices but when I call the  
rownames()
function it returns me a NULL value. It worked perfectly until I had  
to
reinstall the RBloomberg package. Here is my code:
(you need to be connected to bloomberg to run it):
conn <- blpConnect(na.action="na")
prices <- blp(conn, securirtyNames, "PX_LAST", startDate, endDate)

rownames(prices)

NULL

any idea of what it could be? What I don't understand is that I can  
see
those rownames on the console...