I had a custom workflow associated with a content type used by a publishing page, that gave this error
[NullReferenceException: Object reference not set to an instance of an object.] Microsoft.SharePoint.Publishing.Internal.WorkflowUtilities.GetAssociationDataValue(CachedWorkflow workflow, String xmlNodeName) +124
Digging throught the web I found a solution.
We need to had this association data to the workflow
<my:myFields xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:my=\"http://schemas.microsoft.com/office/infopath/2003/myXSD\" xml:lang=\"en-us\"><my:ItemChangeStop>false</my:ItemChangeStop></my:myFields>
Apparently Sharepoint is looking for node called "ItemChangeStop"
Thanks to Julien C (http://www.sharepointdev.net/sharepoint--workflow/sharepoint-error-when-editing-documents-with-custom-content-types-44343.shtml)
Somewhere else people talked about and hotfix from microsot that isn't available on the web ...
