Semantic Error (SEM1037): The data type '...' is not a structure or program organization unit.

A variable that is declared as a "single value" (in contrast to a POU with several inputs and/or output formal parameters), is accessed like a POU formal parameter or a structure element.

Example: MyVar is declared as an INT variable. In the code, this variable is accessed in an invalid way like a structure element or an FB output.