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Error (Safety Specific Code Generator): Illegal data type: '...'.

This error message can have two reasons:

The data type of the accu does not match the data type of the operand, or
a function is connected to a data type which is not allowed.

Remedy:

Double-click the error in the Error List to jump to the suspected worksheet (where the error is marked).
Correct the suspected data type.

Further Info
Refer to the topic "Data Types" for details.