Delete a contenttype from a document library

You can find a lot of information about how to add a contenttype (SPContentType) to a list or document library (SPDocumentLibrary). But how do you delete a contenttype from a document library?

From the administration UI you can remove a contenttype by selecting "Delete this content type" as outlined here:

But how do you do it programmatically?`

If you take a look at SPDocumentLibrary it has a reference to ContentTypes. The collection has a delete operation which takes a GUID of the content type as parameter, as outlined by Microsoft here.

dim oDocLib as SPDocumentLibrary
dim oCT as SPContentType
oCT = oDocLib.ContentTypes("Documents")
oDocLib.ContentTypes.Delete(oCT.Id)

Trying out this code raises an exception:

System.ArgumentOutOfRangeException: Specified argument was out of the range of valid values.
Parameter name: id
at Microsoft.SharePoint.SPContentTypeCollection.Delete(SPContentTypeId id)

Inputs very much appreciated.

I got the idea to try using the Lists.asmx web service as described here by Microsoft. No luck so far.

You can get around the issue as described here. Set the content type programmatically before you add the items - but that is not really the answer long term :-(

Conclusion: Now it works!!!
I tried to delete the Documents content type found in the web collection AvailableContentType i.e. executing the code:

dim oWeb as SPWeb
dim oDocLib as SPDocumentLibrary
dim oCT as SPContentType
oCT = oWeb.AvailableContentTypes("Documents")
oDocLib.ContentTypes.Delete(oCT.Id)

this fails as described above.

The above code works.