Error in Python script node

I have used a Python scripting within my KNIME workflow. Within the configuration window, the code runs successfully but throws and error when trying to actually run the node. Execute failed: Output DataFrame contains duplicate values in its index: ‘0’, ‘1’, ‘2’, and others. This is not supported. Please make sure that each entry in the index (i.e., each row key) is unique. Can you please help me with the solution.