We explore the duality between AdS_3 massive type IIA supergravity vacua and two-dimensional N=(0,4) quiver quantum field theories. After categorizing all kinds of gravity solutions, we demystify the ones that seem to reflect anomalous gauge theories. In particular, we prove that there are bound states of D-branes on the boundary of the space which provide the dual quiver theory with exactly the correct amount of matter in order to cancel its gauge anomalies. Then we propose that the structure of the field theory should be complemented with additional bifundamental matter, which we argue may only be N=(4,4) hypermultiplets. Finally, we construct a BPS string configuration and use the old and new supersymmetric matter to build its holographically dual ultraviolet operator.