Logon Failure: the user has not been granted the requested logon type at this computer

If you see this message the following should be done on the computer containing the shared files.

Download the following and install it: Windows Server 2003 Resource Kit Tools
http://go.microsoft.com/fwlink~?LinkId=4544

After the installation is complete click on: Start | All Programs | Windows Resource Kit Tools | Command Shell

Then enter the following commands. (Attention: they are case sensitive)

net user guest /active:yes
ntrights +r SeNetworkLogonRight -u Guest
ntrights -r SeDenyNetworkLogonRight -u Guest

The first command enables network access for Guest account, the two subsequent ones change two different policies to  allow network access for Guest account.