Can Natsu use his flames to grab things still? He used it that one time in fighting the wind guy when he fell off the railroad tracks.
These has been nothing to indicate that he lost the ability to 'grab' things with his fire...he just hasn't done it since then. The same as how he hasn't made use of his abilities with basic Transformation Magic since he first learned how to do it (by turning into Lucy while tutored by Mirajane).
As for why he hasn't used it since...either the author forgot about it or, as an in-universe perspective, he hasn't needed it. The main reason he pulled that ability out during his fight with Erigor was because he was falling off a bridge and needed to get back. Since then, he seems to have figured out how to use his fire as a form of Jet Propulsion, meaning he can sort-of-fly. Not much need to pull yourself back up onto a bridge by grabbing it with fire, when you can just use your hands as rocket engines.