Within a PS script, I'm trying to add a site column and add this column to a custom content type.

Here is my script :

add-pssnapin Microsoft.SharePoint.PowerShell -EA 0

function AddFieldToContentType([Microsoft.SharePoint.SPWeb] $web, [string]$contentTypeName, [string]$xmlSchema)

    $fieldName = $web.Fields.AddFieldAsXml($xmlSchema)

    $field = $web.Fields[$fieldName]
    $ct = $web.AvailableContentTypes[$contentTypeName]
    $link = new-object Microsoft.SharePoint.SPFieldLink $field


[Microsoft.SharePoint.SPWeb]$web = get-spweb -Identity http://somewhere
[xml]$xml = 'my field schema truncated for readability'

AddFieldToContentType $web "my content type name" $xml

This fails at the line $ct.Update($true) with this error :

Exception calling "Update" with "1" argument(s): "The collection cannot be modified."

What's wrong with this code ?


1 Answer 1


AvailableContentTypes is readonly, so you need to use ContentTypes instead.

$field = $web.Fields[$fieldName]
$ct = $web.ContentTypes[$contentTypeName]
$link = new-object Microsoft.SharePoint.SPFieldLink $field
  • 1
    To add to this, AvailableContentTypes is read only because it is a collection from the current scope, including those of the current website, as well as any parent websites Jul 6, 2011 at 16:09
  • this solved the problem, hovewer, I don't understand the cause, as I'm not changing the content type collection, but the content type itself
    – Steve B
    Jul 6, 2011 at 16:29
  • The Update() method must be looking at the collection that the content type is in and using that in some way. It follows since you can't create a new content type and call Update() without first adding it to a collection - a list or web. AvailableContentTypes gathers them up into a collection for you, but it doesn't give you the collection for the specific web.
    – Laurie
    Jul 6, 2011 at 16:52
  • I get almost this exact same problem: - $ct.update($true) produces an "Access Denied" error, although it does add the Site Column to the Content Type. - however, $ct.update($false) works without a hitch. - not only that, but in both cases, the "update all columns which use this column" is set to Yes. I've no idea why it acts this way.
    – Josh Korn
    Nov 3, 2016 at 15:29

Not the answer you're looking for? Browse other questions tagged or ask your own question.