Excel won't run in PS script from task scheduler

I have a fairly simple two part task that I want to run daily via the task scheduler:

The script below runs fine interactively, however, Excel never launches when run from the task scheduler. It’s as if PowerShell cannot fine the Excel COM object. Excel was installed on this server specifically for this task. It is PS v4 on Windows Server 2008 R2.

$dir = "D:\foo2_sys\ExportCodes"
# Make backup copy of spreadsheet
$lwt = (Copy-Item -Path (Join-Path $dir "EXPORT CODES 2012.xls") `
    -Destination (Join-Path $dir "ExportCodesBackup.xls") `
    -Force -PassThru -ErrorAction Stop).LastWriteTime
"Job run on         $(Get-Date)
Codes last updated $lwt" |
    Out-File -FilePath (Join-Path $dir "timestamp.txt") -Encoding ascii
Remove-Item -Path $dir\ExportCodes.csv -ErrorAction SilentlyContinue
# Convert to CSV for import into shipping programs.
$xl = new-object -comobject excel.application
$xl.DisplayAlerts=$true
$xl.Visible =$false
$Workbook = $xl.workbooks.open((Join-Path $dir "ExportCodesBackup.xls”),0,$True)
$Workbook.SaveAs("$dir\ExportCodes.csv",6)
$Workbook.Saved = $True
$xl.Quit()
[System.Runtime.Interopservices.Marshal]::ReleaseComObject($xl) | Out-Null