adding new folder to share over existing network

I have 3 computers, Winxp. Hard wired. I have several folders shared and they all work fine, with all 3 computers. I needed to share an existing folder today that was not already shared. I set it up to share just like I always do. Now on the other 2 computers I can see the shared folder but get the error message "\\"folder"is not accessible" any idea why it dosen't work? I have rebooted all computers and still dosen't work.

Thanks,
David