Getting error while Installing SQL Server 2008 R2 Express edition

Question

I am trying to do a silent unattended installation of SQL Server 2008 R2 Express edition.

I am using the below code to achieve it

<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi"
  xmlns:util="http://schemas.microsoft.com/wix/UtilExtension">
<Fragment>

<PackageGroup Id="SqlServer2008R2">

<ExePackage InstallCommand="/q /action=INSTALL /IACCEPTSQLSERVERLICENSETERMS=1 /FEATURES=SQLEngine /INSTANCENAME=SQLSERVERINSTANCE /SQLSVCACCOUNT='NT AUTHORITY\SYSTEM' /SECURITYMODE=SQL /SAPWD=abc#Wd1234 /SQLSYSADMINACCOUNTS='NT AUTHORITY\SYSTEM' /ADDCURRENTUSERASSQLADMIN=TRUE /TCPENABLED=1 /NPENABLED=1"
              InstallCondition="VersionNT64"
              DetectCondition="Instance"
              Name="SQLEXPR_x64_ENU.exe"
              Compressed="no"
              Vital="yes"
              PerMachine="yes"
              Permanent="yes"
              Cache="no"
              DownloadUrl="http://download.microsoft.com/download/5/1/A/51A153F6-6B08-4F94-A7B2-BA1AD482BC75/SQLEXPR_x64_ENU.exe"
              >
    <RemotePayload
      Size="77677408"
      ProductName="Microsoft SQL Server 2008 R2 Express"
      Description="Microsoft SQL Server 2008 R2 Express"
      Version="10.50.1600.1"
      CertificatePublicKey="fjhuirh8454850495jffjk5"
      CertificateThumbprint="hfgjhrt758947jjgi58g"
      Hash="584809tgjgjfgjk58ifjufkjjkjfi"
      />
     </ExePackage>
    </PackageGroup>
  </Fragment>
</Wix>

During installation I get this error
arguments: '"C:\ProgramData\Package Cache\2FF1A50B2277987C9CD65B99812CEAF2A67EA362\SQLEXPR_x64_ENU.exe" /q /action=INSTALL /IACCEPTSQLSERVERLICENSETERMS=1 /FEATURES=SQLEngine /INSTANCENAME=SQLSERVERINSTANCE /SQLSVCACCOUNT='NT AUTHORITY\SYSTEM' /SECURITYMODE=SQL /SAPWD=abc#Wd1234 /SQLSYSADMINACCOUNTS='NT AUTHORITY\SYSTEM' /ADDCURRENTUSERASSQLADMIN=TRUE /TCPENABLED=1 /NPENABLED=1' 

Error 0x84b40000: Process returned error:
0x84b40000: Failed to execute EXE package.0x84b40000: Failed to configure per-machine EXE package.Applied execute package: SQLEXPR_x64_ENU.exe, result: 0x84b40000, restart: None [05DC:0B04][2012-12-11T16:25:49]: 

I have Check the parameters on Command promt that i am using in the above code just to check see if i am missing any important parameter that is required for the installation of sql server 2008 R2 express edition but it worked on command promt and installed SQL server 2008 R2 express edition with no problem. but i can't do a unattended installation using all that parameters. Pls help me out i am stuck with it.