samba - Apr 2013 - Samba share on a network shared with other people is randomly accessible

I installed Ubuntu Server 12.04, Samba, configured smb.conf, added a Samba
user, and restarted Samba, to create a shared folder between my VM guest
(Ubuntu), and my host (Windows 7). I also set my Network to Bridged instead
of NAT.

I was able to access \\UBUNTU for a while, but now I'm not able to, and it
seems like randomly I'll be able to access \\UBUNTU for brief amounts of
time.

I'm new to Ubuntu, Samba, VMs, and networking in general, so I tried making
the VM's IP static in hopes it would fix this to no avail.

I'm at a complete loss and have worked on this for 3-4 days straight now.

Here's what I appended to smb.conf:

[my_share]
  path = /home/cory/apps
  read only = no
  admin users = cory

I get the feeling this is a problem with the network changing when other
people connect to it, and/or some Samba settings.

Anyway, I'd love any help. I'm completely stumped as to why it'd
work
sometimes, and why it wouldn't work most of the time - without changing
anything. Thanks!