problem with shared folders

hi!
I have a laptop (FLIP) with XP Professional SP2 connected with a crossover
cable to a desktop (CASA) with XP Home SP2. The desktop connects to the
internet by an adsl connection, wich is shared with the laptop. I have
internet in both computers.

When I run \\flip in order to access the laptop, I am able to see the
laptop's shared folders and their content, altough some files are not
presented.
The reverse doesn't aply, when I run \\casa to acess the desktop I get a
message box with the text:

"\\casa is not accessible. You may not have permission to use this network
resource. Contact the server administrator.

Logon error: it was not given to the user the type of session ask by this
computer."

While researching I discover the following in the desktop security event's
log:

"type of event: failed auditory
event origin: Security
event category: Logon/logoff
event ID : 534
Date: 01-03-2006
time: 6:23:03
User: NT AUTHORITY\SYSTEM
Computer: CASA
Descrition:
Logon error:
Motivo: it was not given to the user the type of session ask by this
computer
name of user: Filipe
Domain: FLIP
Type of logon: 3
Logon process: NtLmSsp
autentication package: MICROSOFT_AUTHENTICATION_PACKAGE_V1_0
Workstation name: FLIP"

So, could anyone please tell me what is going on? Thanks in advance