The message appears if a file with a specific identifier is compiled twice in a single compilation run, as in the following example, where the first compilation is run explicitly (File1.sv file is specified in the alog command), and the second one is run implicitly (the File1.sv is included in the File2.sv with the include directive).
To trigger the error, compile the files with the following command:
alog File1.sv File2.sv
Where File1.sv and File2.sv are as follows:
module m(a); input reg a; endmodule
`include "File1.sv" module top; endmodule