Okay, so I searched EVERYWHERE for a solution to the same error message problem. I have 3 computers networked (two are XP, my host/main computer is Vista Home Premium). After messing with it for hours, I got it! So, here's what I did:
From the Host computer: Open up my Network
Double-click/OPEN the Host computer (my main computer is named "OfficeMgr"
Right click on your SHARED folder (this could also be named PUBLIC maybe)
Select "Properties" from the menu
On the new pop-up properties box, go to the "Sharing" tab
Click "Advanced Sharing"
(If it asks for your permission to continue, click "continue".)
Make sure the SHARE THIS FOLDER box has a CHECK in it.
Verify that the share name (mine says PUBLIC) is the same as the file name you are sharing (this is pretty much a given).
Click on the PERMISSIONS button.
Under Group/User Names: Click on the group or user to want to give access to (mine is called EVERYONE).
Making sure the correct user is still highlighted above, go down to the Permissions box and CHECK the boxes for FULL CONTROL, CHANGE, and READ under the ALLOW permissions column.
Click APPLY, then OK.
OK, now go check your other computer and see if you can save to your Host/Main Computer now!
Hope this helps!