Semantic Error: The function block instance '...' does not exist.
In a code worksheet, a function block instance is used for which no instance name is declared.
In graphical code, the easiest way to enter the declaration directly from the code worksheet into the local 'Variables' table is using the block's context menu.
In the code editor, right-click on the FB instance name above the block icon and select 'Create New Function Block Instance' from the context menu. The declaration is inserted into the local 'Variables' table of the current POU without opening this worksheet. This way, the default name proposed by the editor is declared.
For an FB instance used in textual code, the declaration must be entered manually into the related local 'Variables' table.