Hi,
I understand that you encountered the error message when your clients
connected to some of your SQL Server instances.
If I have misunderstood, please let me know.

To narrow down this issue, could you please first answer me the following
questions:
1. Did you encounter this error when you connected to your SQL Server
instance locally?
    Shared Memory will only be used when you connected to your SQL Server
instance locally, so this issue should not be related to Shared Memory if
you remotely connected to your SQL Server instance.

2. Did your SQL Server instance use a certificate explicitly specified by
you for encryption?
    If you used a certificate, I recommend that you refer to this article
to configure your server and client computers:
    How to: Enable Encrypted Connections to the Database Engine (SQL
Server Configuration Manager)
    http://msdn.microsoft.com/en-us/library/ms191192.aspx

3. If you did not explicitly specify a certificate, what is the result if
you configure your client connection settings "Force Protocol Encryption"
to True and "Trust Server Certificate" to True?
   In this case, SQL Server 2005 instance will generate a self-signed
certificate and you can configure the settings on your clients via opening
SQL Server Configuration Manager on your client computer, right clicking
SQL Native Client Configuration, clicking Properties and then setting the
two options. If you see "No properties are available", that means your
client registry key was messed up and led to the connection error. To fix
this, please reinstall SNAC(SQL Native Client).

Hope this helps. If you have any other questions or concerns, please feel
free to let me know.

Best regards,
Charles Wang
Microsoft Online Community Support
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Hi,
Just a kind reminder, I have not received your response. Please feel free
to post back at your convenience if you need further assistance.

Have a great day!

Best regards,
Charles Wang
Microsoft Online Community Support
=========================================================
Delighting our customers is our #1 priority. We welcome your
comments and suggestions about how we can improve the
support we provide to you. Please feel free to let my manager
know what you think of the level of service provided. You can
send feedback directly to my manager at: msdnmg@microsoft.com.
=========================================================

=========================================================