access is denied on wire-less computer

I have a wire-less home network,which was working find until a couple of
weeks ago.I have xppro-sp2.I have a linksys router,a desktop computer
upstairs & a desktop down-stairs with a linksys wire-less card installed.
Problem:
I enabled filesharing on a folder on my desktop upstairs & also down-stairs.
In my network places it only shows my shared folder upstairs.If i click on
view workgroup computers I can see the icon for the downstairs computer,but
when I click on the icon it states that I cannot connect because I do not
have perrmission contact administrator,access is denied.If I assign a drive
Letter to the same folder using add a network place I then have access to the
folder on the downstairs computer.
On the downstairs computer I can see & access all shared folders everything
is fine.
Anyone?