Semantic Error: The variable '...' does not exist in '...'.
In a textual code worksheet, a function or function block is called with a formal parameter which does not exist in the called POU. The entire function/FB call is underlined in the code. Check all formal parameters and correct wrong spelling/parameters.
For user-defined FUs/FBs, this may be expected because the appropriate variable will be declared later with 'Usage' = 'Input' (VAR_INPUT) or 'Output' (VAR_OUTPUT) or the formal parameter name has been changed meanwhile.