What does it mean "Error at line 0"?

What does it mean "Error at line 0"?

Here is the function that I wrote:
  1. map externalapps.GetCurrentSymptoms()
  2. {
  3.     symptomMap = map();
  4.     for each Symptom_ID in Symptoms [notContains(Symptom_Name,"Deprecated")]
  5.     {
  6.         symptomMap.put(input.Symptom_ID,input.Symptom_Name);
  7.     }
  8.     return symptomMap();
  9. }

When I try to save, it gives me this error:

  Error at line number : 0
Mismatch data type for function 'put' at argument index 2 expected data type STRING found data type Symptoms
I don't really know how to debug this one?

Symptom_ID and Symptom_Name are both just basic text fields in the form Symptoms.