Windows – MSSQLSERVER Exception occurred while enqueueing a message in the target queue. Error 15404, State 19

I am getting a bunch of messages in the Windows Application Event Log. Here is exact text from Event Viewer:

An exception occurred while enqueueing a message in the target queue. Error: 15404, State: 19. Could not obtain information about Windows NT group/user 'myDomain\myDomainusername', error code 0x5.

Event ID: 28005 Source: MSSQLSERVER

Message is emitted twice at what appears to be intervals of 64 seconds.

Server is Windows 2008 R2 Standard. I am logging on to this server as myDomain\myDomainusername. Examining Local users and groups I notice that:

myDomain\myDomainusername is a member of the Local Administrators group

I bring up SQL Server 2008 R2 Management Studio and I see a Login for myDomain\myDomainusername. Server roles checked for this domain username are:

• dbcreator
• public
• securityadmin

Clicking User Mapping puts out a msg:

One or more databases are inaccessible and will not be displayed in list.

..but then the list is displayed and all the Sharepoint databases are listed and checked with Database role membership checked for all as db-owner and public.

I note that master, msdb, and tempdb are NOT mapped to this login.

So, I go back to Server Roles for this myDomain\myDomainusername login and try to add sysadmin server role and I get a message: "user does not have permission to perform this action".

This domain username – myDomain\myDomainusername – was my intended Database Access Account for connecting to the Sharepoint 2010 configuration database and THAT appears to be correct but apparently being a member of the Local Administrators account does not in turn give the sysadmin server role for that same login.

What would be the best way to fix this? First, so these constant messages are stopped and secondly, that I have a decent setup moving forward.

p.s. At this point only SQL server and Sharepoint are installed and I've obviously done something a bit wrong.

EDIT-UPDATE:
OK – I used a different LOGON (a LOCAL administrator) and

• added the sysadmin server role to the properties for the login for myDomain\myDomainUsername as you said to do.
• I noticed that the SQL Configuration had only Shared Memory protocol enabled for the Server – so I enabled Named Pipes and TCPIP which I figured might be useful for obtaining information about a domain user.
• Then I re-booted the server (first Saving / clearing all the event logs).

The problem continues.

If, however, I logon to this server with a local administrator account, then SQL comes up without any of these messages in the Event Viewer.

I am wondering if something about this machine needs to be set in the Domain Controller (i.e. I am not the domain admin but I came across something that looked possibly relevant but I am not trained to properly decipher this:

Setting User Account Control Policy for Delegated Administrators

LATE BREAKING IDEA:

Wondering about meaning of "message in the target queue" I think I found that I need to run sp_changedbowner according to this post:

http://social.msdn.microsoft.com/forums/en-US/sqlservicebroker/thread/28699c94-4d1b-43f2-bcfb-a95152ca226b/

During the Sharepoint Install, I specified myDomain\myDomainusername when the wizard asked for a "database access account" to connect to the configuration database. People seem to fix this problem by changing the db owner to 'sa' or to a local machine account – but I thought Sharepoint wants a domain account for this purpose.

SUMMARY: If this is the problem and the fix, will it be OK with Sharepoint to have this be a local Windows account or the SQL 'sa" account? Sorry about so much typing of more info!