Your Map file didn't tell any information about symbols.
Actually ,Do you use the _distance as a procedure?
if yes it's also need to be declared as public by the parent file(process).

From the message you've been posted I think that you may not delcare it by yourself which mean that it is the component of some of your library(or may be from compiler itself).

Check your symbol "_declare" on any header file.May be you have missed to include symbol.