I am starting to use command line dataloader to import data to the custom object on my org, currently I ran into a problem each time I run the dataloader there will be exception says:

Error while calling web service operation: upsert, error was: Field name provided, does not match an External ID for Portlet__c [InvalidFieldFault [ApiQueryFault [ApiFault exceptionCode=''INVALID_FIELD' exceptionMessage='Field name provided, does not match an External ID for Portalet__c']

Since I dont specify the external id for that object,  are there any stuffs I need to be aware about the csv file format? Thanks!

Sincerely

theMythical