I can create new folders on my Windows XP machine, set them to "shared".

On my Mac, I pick Finder → Go → Connect to Server → smb://192.168.1.4 → Connect → Name / Password.

It even shows me all the names of the newly created shared-folders on my PC, but when I try to actually connect to any of them I get

connection failed, there was an error connecting

Any idea on what would cause that? The fact that it successfully gets so far—to actually showing me my PC share-names—must mean I have 99% of this working correctly, i.e. the physical connection, the IP address, the user name, the password, etc.

Still, I can't seem to access the folders themselves.

I've tried this with my Windows XP firewall on/off, and Norton AntiVirus on/off. Same problem.

Everything did work fine, 4 months ago. Were there any odd OS X or Windows updates released recently? I always apply them all.

smbclient on the Mac does correctly find the XP machine, my XP user name, and accepts my XP password.

I get the following from that smbclient command:

Doing spnego session setup (blob length=16)
server didn't supply a full spnego negprot
Got challenge flags: ...
Got NTLMSSP flags: ...
Got NTLMSP flags: ...
Domain=[XPMACHINE] OS=[Windows 5.1] Server=[Windows 2000 LAN Manager]
tree connect failed: NT_STATUS_INSUFF_SERVER_RESOURCES

I'm not sure why a standard XP box can't "supply a full spnego negprot". Whatever that means.

Using XP's RegEdit to change my IRPStackSize from 11... to 13, 15, 20, 22... still gives that "NT_STATUS_INSUFF_SERVER_RESOURCES" error on the Mac.