4GL converts between one data type and another automatically whenever it can do so without losing information. In the current statement, it could not do so. Look first for function calls, and inspect the values that are passed as parameters. Check that the values that are passed agree in type with the parameters as they are defined in the function bodies. (An example of such an error would be calling a function fun("X") when within the function its parameter was defined as an integer.) If the statement is a LET statement, check that the value that is computed on the right can be accommodated in the variable that is named on the left.