"Failed to Write to Client Mailslot" Error

No longer supported
Zoo 4.0 was the license manager for Rhino 4, which reached end of life long ago. This article is kept for historical reference. For current LAN Zoo licensing, see the LAN Zoo guide.

Question

I have installed the Zoo on one of our servers. But none of my Rhino clients can obtain a license. When I look in the Zoo’s log file, I see the following errors:

<date> <time>  ERROR: Failed to write to client mailslot on: <computer>
<date> <time>  LAST ERROR 183: Cannot create a file when that file already exists.

Answer

The error message indicates that the Zoo was able to create a mailslot but was unable to write to it.

Resolution

  1. Verify that Client for Microsoft Networks is both installed and enabled on the Network Connection on the system running the Zoo.
  2. Verify that Enable NetBIOS over TCP/IP is checked in the advanced TCP/IP options of Network Connection on the system running the Zoo.
  3. If the computer running the Zoo is also running a firewall, make sure that UDP Ports 137 and 138 and TCP Port 139 are open.
  4. If there are one or more routers between your Rhino systems and the Zoo, make sure that UDP Ports 137 and 138 and TCP Port 139 are open on those routers too.
  5. Verify that the system running the Zoo server can “see” other systems on your network. In other words, verify that name service lookup, either DNS or WINS, is working.

Note that these are known fixes for this problem. The error, “Cannot create a file when that file already exists”, is a common Windows error. So, it is possible that the resolution to this problem, in your situation, might be something other than what is listed above.