"Fields cannot be mapped" when trying to map 2 custom fields before initial SFDC sync

Hi,

We are in the process of setting up our initial sync with SFDC. We have some custom fields on the lead that also exist on the account and they are properly mapped in SFDC before I brought them over to Marketo by connecting with my marketo sync user.

When the fields got created in Marketo, it created the fields with appending (A) and (L) to the field name. I read on some other posts that if the API name between the lead and account field does not match then that could happen. While that is the case for a few of the fields, it is not true for all of them. When I try to drag the fields on top of each other to map them as outlined in the Marketo documentation, I get the error message "Fields cannot be mapped". The fields are of the same field type, are mapped in SFDC properly and in many (but not all) cases the API field name matches between the 2 objects.

Since the mapping apparently is a one time shot according to Marketo documentation, once the sync is started, the mapping can no longer be changed, we need to sort this out asap.

Does anyone have any insight? We also reached out to Marketo directly but was hoping someone here had any pointers.

Thanks

Ines