C1003   Ambiguous variable reference

     Explanation:  You referred to an undeclared or unaliased variable
     when compiling with the /W option.  This includes variables you specify
     within PRIVATE, PUBLIC, or PARAMETERS statements and not declared MEMVAR
     or referred with the MEMVAR -> alias.  Declaration statements include
     FIELD, LOCAL, MEMVAR, or STATIC.

     There are several special cases where this warning can occur:

     1. When compiling program (.prg) files containing @...GET, CLEAR, CLEAR
        ALL, READ, or READ SAVE commands, a warning will be generated for the
        system variable GetList.

     2. When compiling program (.prg) files containing database commands such
        as AVERAGE or SUM, a warning will be generated for undeclared result
        variables.

     Note:  This warning is often followed by the "C1004 Ambiguous
     reference, assuming memvar" warning message.

     Action:  In general, declare all variables used in a procedure or
     function.  If the variable is a database field, specify the variable
     prefaced by the work area, and declare it within a FIELD statement.

     If the warning refers to the system variable GetList, declare it within
     a MEMVAR statement either at the top of the current procedure or
     function, or at the top of the current program (.prg) file if you are
     compiling with the /N option.