In an ST code worksheet, the lexical analysis detected a code construct which cannot be resolved. For example due to a invalid character, the system is not able to classify this code part, i.e., it cannot determine the token type (e.g., operator, identifier, ...) for it. The affected code position is underlined in the worksheet.
Refer to the topic "IEC 61131 Implementation - Identifiers" for details on the naming conventions for identifiers.