IPADDRESS/SLASH Help

Hi Scripting Guys,

I've got a script which works perfectly on Win8 but fails on Win7 which must be down to the PS version, I am using V2.0 on Win 7

The error I get is as follows

Method invocation failed because [System.String] doesn't contain a method named 'G
etAddressBytes'.
At line:169 char:29+  $SubnetMask.GetAddressBytes <<<< () | ForEach-Object { [Convert]::ToString($_, 
2) } + CategoryInfo          : InvalidOperation: (GetAddressBytes:String) [], Runt 
   imeException+ FullyQualifiedErrorId : MethodNotFound

My script is as follows..

function ConvertTo-MaskLength {<#
    .Synopsis
      Returns the length of a subnet mask.
    .Description
      ConvertTo-MaskLength accepts any IPv4 address as input, however the output value 
      only makes sense when using a subnet mask.
    .Parameter SubnetMask
      A subnet mask to convert into length
  #>

  [CmdLetBinding()]
  param(
    [Parameter(Mandatory = $True, Position = 0, ValueFromPipeline = $True)]
    [Alias("Mask")]
    [Net.IPAddress]$SubnetMask
  )

  process {
    $Bits = "$( $SubnetMask.GetAddressBytes() | ForEach-Object { [Convert]::ToString($_, 2) } )" -replace '[\s0]'

    return $Bits.Length
  }
}

if(Test-Connection -ComputerName $Computer -Count 1 -ea 0) {
   $Networks = Get-WmiObject Win32_NetworkAdapterConfiguration -ComputerName $Computer | ? {$_.IPEnabled}
   foreach ($Network in $Networks) {
    $IPAddress  = $Network.IpAddress[0]
    $SubnetMask  = $Network.IPSubnet[0]
    $DefaultGateway = $Network.DefaultIPGateway
    $DNSServers  = $Network.DNSServerSearchOrder
    $IsDHCPEnabled = $false
    If($network.DHCPEnabled) {
     $IsDHCPEnabled = $true
    }
    $Bits = "$( $SubnetMask.GetAddressBytes() | ForEach-Object { [Convert]::ToString($_, 2) } )" -replace '[\s0]'

    $slash= $Bits.Length
    $ipslash = "$IPAddress\$slash"
    $MACAddress  = $Network.MACAddress
    Write-Host "Computer Name    : $Computer"
    Write-Host "IP address       : $IPAddress"
    Write-Host "IP address/slash : $ipslash"
    Write-Host "Subnetmask       : $SubnetMask"
    Write-Host "default gateway  : $DefaultGateway "
    Write-Host "DNS Servers      : $DNSServers"
    Write-Host "MAC ADDRESS      : $MACAddress"
    }
    }

Do you know how I could get this to work on PS2.0? 

Thanks in advance

Joe