asymettrical Windows sharing behaviour

What would cause a couple of Windows XP or 2000 computers connected via
a workgroup not to be able to share files equally with each other?
Specifically, I got a laptop and a desktop, each one has various file
shares available. When I mount one of the laptop's folders onto the
desktop, it connects and it can list all of the files, but as soon as I
try to copy or move a file from laptop to the desktop (i.e. pull from
the laptop into the desktop) it comes back saying that the disk is write
protected. However, when I mount the desktop's file system into the
laptop, and I do the same action from the laptop side (i.e. push the
file to the desktop from the laptop), it works fine.

I checked the file sharing attributes on the shared directories, and
they're all listed as full read/write access. They're also running the
Windows XP SP2 firewall in both cases.

  Yousuf Khan<!-- ~MESSAGE_AFTER~ -->