E2038 Illegal character in input file - '%s' (%s) (Delphi)

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The compiler found a character that is illegal in Delphi programs.

This error message is caused most often by errors with string constants or comments.

program Produce;

begin
  Writeln("Hello world!");   (*<-- Error messages here*)
end.

Here a programmer fell back to C++ habits and quoted a string with double quotes.

program Solve;

begin
  Writeln('Hello world!');   (*Need single quotes in Delphi*)
end.

The solution is to use single quotes. In general, you need to delete the illegal character.