When trying to sync updates to your salesforce.com instance from Marketo you see one of the following errors in the activity log :
This is an error sent to Marketo from Salesforce. There are a number of reasons why this error could occur.
INSUFFICIENT_ACCESS_ON_CROSS_REFERENCE_ENTITY means that the user who is trying to make the update does not have access to a related element that is required for the record to be updated and saved in SFDC. There are a number of specific examples of what might be the cause but these will vary from organisation to organization depending on the configuration of your salesforce.com. If you were to connect to sfdc as the Marketo user and try manually updating the same record that Marketo is trying to update then you will get the same error in the salesforce.com UI.
Here are a list of some elements that you should check in SFDC if you see this error: