Call a function in a new PS window and passing parameters to it.

I am trying to call a function that adds an outlook calendar event; however, I have to call the function using different creds.  so, I was trying this:

$daystodeletebackup = 30
$date = (get-date).AddDays($daystodeletebackup) 
$newdate = $date.ToString('MM/dd/yyyy HH:mm')
$newdate
$DatabaseName = "Database"
$SQLInstanceName = "Server"

$creds = Get-Credential

Start-Process powershell.exe -Credential $creds Add-CalendarMeeting -subject "DELETE BACKUP FILE" -Body "DELETE Backup File from DECOMMISSIONED database $DatabaseName on Server $SQLInstanceName" -Location $SQLInstanceName -MeetingStart $newdate -Reminder 30

But I get an error: System.Management.Automation.ParameterBindingException: A parameter cannot be found that matches parameter name 'subject'

If I run it and comment out everything past Add-CalendarMeeting it will work but I have to enter in the parameters.  Is there anyway for me to pass the parameters into the new PS window?