The Generate Runtime Code wizard could not calculate the COMMAREA length automatically for the Invoke nonterminal node specified in the error message.
In the generation properties editor, for the flow node specified in the error message, in the Maximum COMMAREA Length field, you selected Generate length value, a selection that should cause the Generate Runtime Code wizard to calculate the maximum length of the COMMAREA automatically. However, in this case the wizard could not calculate that length. Therefore you must calculate the length manually and type it into the field.
See Generation properties of the LINK with COMMAREA invoke type.