Using EWS to work with mail items from a range derived from Get-Date

I am attempting to write a powershell script that uses EWS to move items from the prior month and create a folder named after that month to hold those items. 

I am finding that the search filter only likes the format if you use .NET system.DateTime and not Get-Date.

However it's strange, for testing I configured my variable to be the exact same format as the .NET format but it rejects it. 

The error i receive is: 

Exception calling "FindItems" with "2" argument(s): "The specified value is
invalid for property."
At line:1 char:1
+ $frFolderResult = $InboxFolder.FindItems($sfCollection,$view)
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : ServiceResponseException

For example, if i set $startdate and $enddate like this  $startdate=(([system.DateTime]::Today.AddDays(-60)))

$startdate returns Monday, January 20, 2014 12:00:00 AM, and the search filter works fine.

but if i set $startdate using this: $startdate = (Get-Date).AddMonths(-1).ToString("dddd, MMMM 01, 12:00:00 AM")

It gets rejected event though the output is exactly the same.

i.e. Friday, February 01, 2014 12:00:00 AM

Any help would be appreciated. 

Thank You. 

#Set the mailbox that this script will run against

$MailboxName = "mymailbox@mydomain.com"

# Set up the API dll path, AutoDiscover URL and AD account used to access the mailbox

Import-Module "C:\Program Files\Microsoft\Exchange\Web Services\2.0\Microsoft.Exchange.WebServices.dll"
$service = new-object Microsoft.Exchange.WebServices.Data.ExchangeService([Microsoft.Exchange.WebServices.Data.ExchangeVersion]::"Exchange2010_SP2")
$windowsIdentity = [System.Security.Principal.WindowsIdentity]::GetCurrent()
$sidbind = "LDAP://<SID=" + $windowsIdentity.user.Value.ToString() + ">"
$aceuser = [ADSI]$sidbind
$service.AutodiscoverUrl($aceuser.mail.ToString())

# Determine if the script is running in January in order to set the year used in the search filter

if ((Get-Date).Month -eq 1) {

$searchyear = (Get-Date).Year - 1
}
   Else{
   $searchyear = (Get-Date).Year
   }
      
# Set variables for the search filter to move items from the prior month to a folder

$startdate = (Get-Date).AddMonths(-1).ToString("dddd, MMMM 01,")
$startdatetime= "$startdate $searchyear 12:00:00 AM"
$enddate = [System.DateTime]::DaysInMonth($(Get-date).Year, $(Get-date).Month -1)
$priormonth = (Get-Date).AddMonths(-1).ToString("dddd, MMMM")
$enddatetime = "$priormonth $enddate, $searchyear 11:59:59 PM"


# Set up folder path locations for the search filter

$folderid = new-object  Microsoft.Exchange.WebServices.Data.FolderId([Microsoft.Exchange.WebServices.Data.WellKnownFolderName]::Inbox,$MailboxName)
$MailboxRoot = new-object  Microsoft.Exchange.WebServices.Data.FolderId([Microsoft.Exchange.WebServices.Data.WellKnownFolderName]::MsgFolderRoot,$MailboxName)
$InboxFolder = [Microsoft.Exchange.WebServices.Data.Folder]::Bind($service,$folderid)


# Create the search filter

$Sfgt = new-object Microsoft.Exchange.WebServices.Data.SearchFilter+IsGreaterThan([Microsoft.Exchange.WebServices.Data.ItemSchema]::DateTimeReceived, $startdatetime)
$Sflt = new-object Microsoft.Exchange.WebServices.Data.SearchFilter+IsLessThan([Microsoft.Exchange.WebServices.Data.ItemSchema]::DateTimeReceived, $enddatetime)
$sfCollection = new-object Microsoft.Exchange.WebServices.Data.SearchFilter+SearchFilterCollection([Microsoft.Exchange.WebServices.Data.LogicalOperator]::And);
$sfCollection.add($Sfgt)
$sfCollection.add($Sflt)

# Perform the search

$view = new-object Microsoft.Exchange.WebServices.Data.ItemView(5000)
$frFolderResult = $InboxFolder.FindItems($sfCollection,$view)

# define the destination folder name, check if the destination folder exists


$foldermonth = (Get-Date).AddMonths(-1).ToString("MM")
$newFolderName = "$foldermonth$searchear" 
$fvFolderView = new-object Microsoft.Exchange.WebServices.Data.FolderView(10)
$SfSearchFilter = new-object Microsoft.Exchange.WebServices.Data.SearchFilter+IsEqualTo([Microsoft.Exchange.WebServices.Data.FolderSchema]::DisplayName,$newFolderName)
$findFolderResults = $service.FindFolders($MailboxRoot,$SfSearchFilter,$fvFolderView)

# Create the destination folder if necessary

if ($findFolderResults.TotalCount -eq 0){
		$NewFolder = new-object Microsoft.Exchange.WebServices.Data.Folder($service)
		$NewFolder.DisplayName = $newFolderName
		$NewFolder.Save($MailboxRoot.Id.UniqueId)
}
	else{
		# Folder Already Exists - Do Nothing
	}

# Move the items in to the destination folder

foreach ($miMailItems in $frFolderResult.Items){
   "Moving" + $miMailItems.Subject.ToString()
   [VOID]$miMailItems.Move($NewFolder.Id.UniqueId)
}