Error when running permissions script

Hi

I get the following error when I run the permissions script:

"Method invocation failed because [System.Management.Automation.PSObject] doesn't contain a method named 'op_Addition'."

Code
=====

Function Get-Path($entity){
   $path = $entity.Name
   while($entity.Parent -ne $null){
      $entity = Get-View -Id $entity.Parent
      if($entity.Name -ne "vm" -and $entity.Name -ne "host"){
         $path = $entity.Name + "\" + $path
      }
   }
   $path
}

$si = Get-View ServiceInstance
$am = Get-View $si.Content.AuthorizationManager

$roleList = $am.RoleList

# Create the role map
$roleMap = @{}
# Add the roles to the map
foreach ($role in $roleList)
{
   $roleMap[$role.RoleId] = $role
}

$permissions = $am.RetrieveAllPermissions()
# Foreach permission
foreach ($permission in $permissions)
{
  $roleName = $roleMap[$permission.RoleId].Name
   $entityView = Get-View $permission.Entity
  $report =+ $permission | Select-Object @{Name="Principal"; Expression={$permission.Principal}},
   @{Name="RoleName"; Expression={$roleName}},
   @{Name="Object"; Expression={Get-Path $entityView}}
}

$report | Convert-HTML | Out-File D:\perms.htm