Salesforce - Error Inserting New Opportunity for an Existing Account

Hi All,

Relative Pentaho/Salesforce newbie here....

For a pre-sales demo I'm trying to write a job that allows me to raise new opportunities for existing account in SFDC using the SF 'Insert' plugin. I've managed to get this to successfully insert a completely new record without any link to an existing account. However, as soon as I try to link the new opportunity to an existing account I get the following error:

INVALID FIELD Error Message: The external foreign key reference does not reference a valid entity: Account

I notice there aren't any examples in the help for the SalesForce insert plugin, in either of two of the 'popular' textbooks and I also couldn't find an obvious tutorial on YouTube! Reading around the subject, does the solution involve using the External ID option in some way?

Thanks in advance,

Will