Why SCCM 20012 Install fails with remote 64 bit SQL Server but proceeds for remote 32 bit SQL Server

Question

I have the following setup:
AD User accounts
- SQLAdmin (used to run SQL Services i.e. Database Engine)
- SCCMADmin (used to install SCCM 2012)
SPN registered for user account SQLAdmin
setspn -S MSSQLSvc/SQL.Domain_Name:1432 Domain_Naem\SQLAdmin
setspn -S MSSQLSvc/SQL:1432 Domain_Name\SQLAdmin
setspn -S MSSQLSvc/SQL.Domain_Name:1433 Domain_Naem\SQLAdmin
setspn -S MSSQLSvc/SQL:1433 Domain_Name\SQLAdmin
and checked with setspn -L TESTING\SQLAdmin
1 SERVER called SQL
32bit Server with SQL Server 2008 + SP3 + Cumulative Update 6
2 SQL instances - Default (MSSQLSERVER) and
SCCM2012
MSSQLSERVER instance uses TCP port 1433
SCCM2012 Instance users TCP port 1432 (no dynamic ports)
User accounts that have been given public and sysadmin SQL server roles
on both instances are: SQLAdmin, SCCMAdmin, Domain Administrator, Local Administrator and computer account SCCM
Client Protocols TCP enabled (and Named Pipes) (checked via SQL Server Configuration Manager)
Local Administrators Group on this server has members - SQLAdmin, SCCMAdmin, Domain Administrator, Local Administrator and computer account SCCM
Firewall turned on with access allowed on Ports 1432, 1433, 4022,445, and WMI - WMI-in, DCOM-in and ASync-iN builtin rules allowed\enabled.
1 SERVER called SQL3
64bit Server with SQL Server 2008 + SP3 + Cumulative Update 6
2 SQL instances - Default (MSSQLSERVER) and
SCCM2012
MSSQLSERVER instance uses TCP port 1433
SCCM2012 Instance users TCP port 1432 (no dymanic ports)
User accounts that have been given public and sysafmin SQL server roles on both instances are:
SQLAdmin, SCCMAdmin, Domain Administrator, Local Administrator and computer account SCCM
Client Protocols TCP enabled (and Named Pipes) (checked via SQL Server Configuration Manager)
Local Administrators Group on this server has members - SQLAdmin, SCCMAdmin, Domain Administrator, Local Administrator and computer account SCCM
Firewall turned off
1 SERVER called SCCM
64bit Server that is to be the Primary Site Server\MP for SCCM 2012
ODBC link to SQL\SCCM2012,1432
ODBC link to SQL3\SCCM2012,1432
ODBC uses SQL Native Client 10.0 (64 bit)
Both ODBC connections when TESTed pass and suggest connectivity to SQL Servers
Install process doe SCCM2012
Tried to install SCCM 2012 RC2 when logged in to SCCM Server as AD user account
SCCMAdmin,  and when utilising the SCCM2012 SQL instance on
32 bit server of SQL install proceeds barring warning about 8GB rec, for SQL Server. Then fails on PKI certificate issue. Installation (chose HTTP for MP). I beleive the PKI failure as install starts is
due to the fact that SCCM 2012 needs its database server to b 64 bit ?
Thus i then tried to install SCCM 2012 RC2 when logged in to SCCM Server as AD user account SCCMAdmin,  and
when using the SCCM2012 SQL instance on
64 bit server of SQL install proceeds but fails at checking stage and says:
SQL Server sysadmin rights FAILED SQL3.Domain_Name
Either the user account running Configuration Manager Setup does not have sysadmin SQL Server role permissions on the SQL Server instance selected for site database installation, or the SQL Server instance could not be contacted to verify permissions. Setup
cannot continue.
and
Site System to SQL Server communication  WARNING SCCM.Domain_Name
A communication error has been detected between the specified site system and the site database computer. This error can occur when the site database server is offline or if a valid SPN has not been registered in Active Directory Domain Services for the SQL
Server instance hosting the site database. Setup cannot continue.
Why does the install of SCCM 2012 with 32 bit SQL proceed further than the install with 64 bit SQL, with the latter process failing as above error meesages show and yet both servers are set identically (apart from temporary turning off Firewall on the 64 
bit server) and during the install the Databse Server specified is accepted ?

Answer 1

Thanks for the reply.
I can connect via ODBC to the the 32 bit SQL Server and the 64 bit SQL Server from the SCCM Server
The SQL Server Unit called SQL3 unit is a 64 bit SQL.
The SQL Server Unit called SQL is only 32 bit, but at least gets past the final checking stage and the error messages about sysadmin rights and Site System to SQL Server communication problem, and then fails with PKI certificate error message. 
When trying to install SCCM specifying the 64 bit SQL Server as the Database Server it gives the 2 error messages at the final checking stage of the installation as listed.
So as I said what is confusing is the fact that if the SCCM install uses the remote 32 bit SQL Server it passes the final checking (although fails with PKI certificate message) but the 64 bit SQL Server set up exactly the same apart from the Firewall being
left off for the time being, fails at the final check stage with the 2 listed errors.
If I use a local 64 bit SQL Server the installation is fine.
Still would like to find out what cause the 2 issues for the remote 64 bit SQL Server, when ODBC seems fine, sysadmin rights have been given for the installer account and the SCCM computer account and SPNs have been set for the user account running the SQL
Services.