Problem with mDot library

hello ,

I developped a project using the mbed online compiler and the mDot board so I imported the mDot library “libmDot” but I got this error : “Error: Undefined symbol mbed::Ticker::setup(unsigned) (referred from /src/libmDot/libmDot.ar(mDot.o)).” although i have already used it in another project and it worked.
I don’t understand what’s going on ??

thanks in advance