Hi Melinda,
I apologize we couldn't help you with this one initially. This issue is the result of the sync user having insufficient permissions to access a Record Type which Marketo is trying to attach to the record being synched. ‘Insufficient access’ may also indicate that the record type doesn’t exist. To see which record type is failing, grab the ‘Record Type ID’ value from a failed sync in Marketo, then go into the client’s SFDC instance with a System Admin profile and navigate to xxx.salesforce.com/setup/ui/recordtypefields.jsp?id={PasteRecordTypeIDHere} This will show you if the Record type exists, and which Object it’s associated to, or if the record type does not exist. To change a user’s record type permissions, go to Manage Users>Profiles>Record Type settings then go to the correct object, and give the sync user access to the Record Type. If the record type does not exist, you should clear this value in Marketo to prevent the error from recurring.