Some remarks on the free fields realization of the bosonic string on   AdS3
  We discuss the classical solutions of the equations of motion and the possible boundary condition for a bosonic string with Kalb-Ramond background in AdS3. It turns out that there exists three different physical sectors and that it is also possible to describe the motion on an extremal black hole background. The existence of three sectors clearly shows how one of the spectra proposed is incomplete. We consider also the classical 'canonical' transformation which maps the string fields to the classical Wakimoto ones. It turns however out that the Wakimoto fields are not free because of the boundary conditions and in order to have the usual mode expansion with reasonable behaviour under complex conjugation it is necessary to consider the complexification of AdS3 and then add some constraints. Furthermore they cover only half AdS3 and we need different patches to cover the whole space and to make the above mentioned transformation really canonical. 
Igor Pesando