Sometimes Windows can really drive you crazy … It hadn’t been too long since I had managed to make my shared files accessible to everyone on the network without entering a password, but now it was again broken, although I hadn’t changed any settings since then. Again, I was prompted for username and password when attempting to access shared files, which was exactly what I did not want. After some hair-tearing and cursing, I found the solution, which seems (once more) completely insane and incoherent and would never come to a normal user’s mind. Maybe it helps one or another who is also despairing of this.

To determine whether the error described here is the reason for the sharing problems, you should take a look at the Event Viewer. It can be found under Start → Settings → Control Panel → Administrative Tools → Event Viewer → System. Click through the errors marked with a red icon, watching for the message: “The Server’s configuration parameter "IRPStackSize" is too small for the server to use a local device. Please increase the value of this parameter.” If you find it, there is a good chance that this is the cause for the non-functioning Windows file shares!

This is the official solution proposed by Microsoft:

1. Click Start, and then click Run.
2. Type regedit, and then click OK.
3. Navigate to the following key:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\LanmanServer\Parameters
4. In the right pane, double-click the IRPStackSize value.
   NOTE: If the IRPStackSize value does not already exist, use the following procedure to create it:
1. In the Parameters folder of the registry, right-click the right pane.
2. Point to New, and then click DWord Value.
3. Type IRPStackSize.
   IMPORTANT: Type “IRPStackSize” exactly as it is displayed because the value name is case-sensitive.
5. Change the Base to decimal.
6. In the Value Data box, type a value that is larger than the value that is listed.
   If you created the IRPStackSize value using the procedure described in step 4, the default value is 15. It is recommended that you increase the value by 3. Therefore, if the previous value was 11, type 14, and then click OK.
7. Close the Registry Editor.
8. Restart the computer.

If the problem persists after you complete the preceding procedure, try to increase the value of IRPStackSize even more. The maximum value for Windows 2000 is 50 (0x32 hex).

I first tested a value of 15 as described, but the problem still existed. Then I tried 30, and lo and behold: As if by magic, all my file shares worked again without a password, as desired! Hurray! By the way, I found this tip here.