Invalid File type error when inserting data into MS CRM

When trying to insert data into into MS Dynamics CRM i am getting Invaid File type error. The data i am trying to insert is a GUID. My source is a SQL table, i have a look up to a mapping table to get the guid, preview on the destination looks ok, but when i run my dataflow nothing gets inserted into destinaiton and i get an error "Invalid file type".