It is said in this wikipedia article (in the 7th paragraph) that where there exists huge masses and very large gravitational forces (like around binary pulsars), general relativistic effects can be observed better:
By cosmic standards, gravity throughout the solar system is weak. Since the differences between the predictions of Einstein's and Newton's theories are most pronounced when gravity is strong, physicists have long been interested in testing various relativistic effects in a setting with comparatively strong gravitational fields. This has become possible thanks to precision observations of binary pulsars.
But here in whystringtheory.com (in the last paragraph), it is said that
For small spacetime volumes or large gravitational forces Einstein has little to offer
I know that in singularities, GR fails and this is a motivation for quantum gravity theories. But the second quote above says in small spacetime volumes or large gravitational forces.
Is there any problem with general relativity in conditions with very large gravitational forces (in big enough volumes of spacetime)?