I did not find any errors in this study. This means that I must
accept its revolutionary conclusions: Two versions of the R. Newton's
and P. Sabatier's (NS) scheme for inverting fixed-energy phase shifts
as published in their respective books [4] and [2] are mathematically
incorrect. The Ramm's presentation of this result is concise, well
written and persuasive, with the main conclusion that the NS
procedure cannot be justified even as an approximate inversion
procedure. At the same time, as long as the typical Ramm's argument
concerns the possibilities of an emergence of unacceptable solutions
in certain not entirely ``physical" classes (like $L_{1,1}$), one
still feels that the very core of the NS recipe might remain useful
and valid after its appropriate more rigorous re-formulation, with
all its criticised ambiguities carefully removed. After all, some of
their well known less subtle forms were also mentioned and discussed
by R. N. himself in [4].

Ramm, Alexander G. Analysis of the Newton-Sabatier scheme for
inverting fixed-energy phase shifts. Appl. Anal. 81, No.4, 965-975
(2002). [ISSN 0003-6811; ISSN 1563-504X]

http://www.tandf.co.uk/journals/titles/00036811.html