"Invalid Input" when submitting Request

"Invalid Input" when submitting Request

Hi, 

I have a customize request template with an additional picklist auto-populate from CSV file. 
After filling up the form and upon submission of request. Got the following message: 
  1. response_status: {status_code: 4000,…}
    1. messages: [{status_code: 4001, field: "udf_pick_3308", type: "failed", message: "Invalid Input"}]
      1. 0: {status_code: 4001, field: "udf_pick_3308", type: "failed", message: "Invalid Input"}
        1. field: "udf_pick_3308"
        2. message: "Invalid Input"
        3. status_code: 4001
        4. type: "failed"
    2. status: "failed"
    3. status_code: 4000

Can anyone assist on this. 
Thanks!

Law