When LINGO generates a model, it determines if a variable can be solved for directly and substituted out of the model. These variables are referred to as being fixed, and the row in the model used to solve for a fixed variable is referred to as a fixed row. When LINGO solves for the value of a fixed variable in its fixed row, it will look around a neighborhood of the variable’s value to determine if multiple roots exist, and displays this message if any are found. An example of an equation with such multiple roots would be: @SIGN( X) = 1. All non-negative values of X would satisfy this relation. LINGO will display the names of up to three variables and their corresponding fixed rows with this symptom. LINGO will continue to process the model, however. You should examine the model closely when this error occurs, because it would be unusual to find a well formulated model displaying this characteristic. Keep in mind that there might be a better solution involving a different value for the fixed variable than was chosen by LINGO.