{PCINFO TIP:} Recently found this error will occur on a Vista machine when trying to access an admin or manual share.  Usually due to the XP machine has enough drives the IRPStack has ran out and needs increasing.

I recently had this problem and it was a simple fix actually. 

Problem:  You have a shared directory on a XP Home machine(1) and when you try and access it from one of your other computers, let's call it POS, you get an error.  The funny thing is you can access XP Home machine(1) from POS.
  Well what is actually happening is POS has the directory shared but he doesn't have enough resources to allow you to access it.  Let's say POS is a single minded machine right now and it doesn't have enough attention span to do more than one thing.
  Microsoft has an article explaining the problem you can read at, http://support.microsoft.com/kb/177078/en-us

Fix:
  To verify the following procedure is what you need to do, go to the Event Viewer, on POS, and look for the following  Error in System:
NOTE: To open the Event Viewer, click here to go to the How to Open the Event Viewer area of PCINFO:

Type: Error      Source: Srv     Event ID: 2011
Description:  The server's configuration parameter "irpstacksize" is too small for the server ...

NOTE: You'll notice is use ... when I'm too lazy to finish the sentance and I've given you enough to find it.

  To fix the problem do the following:

1. Select Start > Run and type regedit in the Open: field, then click the Ok button.
2. In the Registry Editor Window expand each of the following by click the + to the left of it.
+HKEY_LOCAL_MACHINE
   +SYSTEM
     +CurrentControlSet
       +Services
         +lanmanserver
3.  In the left pane, select parameters
4.  In the right pane, double click IRPStackSize.
5.  In the Edit DWORD Value window, select the Decimal radio option
6.  In the Value data: field the value needs to be increased, usually by increments of 5. 
Example: If the value is 11 change it to 15.  If the value is 14 or 15 change it to 20...
7.  Click on the OK button, then close the Registry Editory window.
NOTE: Now the Server service needs to be restarted for the new setting to take effect.
8.  Select Start > Run and type services.msc in the Open: field, then click the Ok button.
9.  In the Services Window's right pane, scroll down to the item in the Name column called Server
10. Right click on Server and select Restart       {PCINFO TIP: You can also do this by selecting the button on the Services toolbar.}
11. If a Restart Other Services window appears, click on the Yes button. 

  Now the new IRPStackSize setting on POS should be ready.  Make sure you close the Explorer window(s) on the XP Home machine(1) you were trying to access the share on POS with and try and access the share again.  Yes you'll have to open the window I just had you close, but there was a reason for that.
  If you still get the error, repeat the steps above and increase the IRPStackSize by 5 again.  Usually from what I've seen in XP Home the size is 11 and on XP Pro it's 30.