The UK's advertising watchdog has upheld a complaint that the electronics chain had encouraged viewers to believe they could watch ultra-high definition broadcasts of the Euro 2016 football championship.
It follows an earlier rebuke about an advert shown in 2014.
Content in 4K is still relatively uncommon, posing a challenge to stores.
The format is marketed as providing four times as much detail as 1080p high definition transmissions, because the screens have that many times more pixels.
Sky's recent launch of its Ultra HD service last week has improved matters. But until then, BT was the only broadcaster transmitting 4K content to UK audiences and its offering was often limited to one football match a week.
Other alternatives include a limited number of shows and films on streaming services including Netflix, Amazon Instant Video and YouTube.
Currys PC World - which is owned by DSG Retail - screened the most recent of the two offending adverts on 4 June, six days before the Uefa (Union of European Football Associations) competition began.
"We know some people will do whatever it takes to watch the football on the right TV," stated the voiceover, before providing details of two 4K televisions.
The advert did not explicitly refer to Euro 2016, but the Advertising Standards Authority (ASA) noted that it had contained a graphic of a rotating football made up of the flags of the various competing teams.
Part of the store's defence was that, even though the Euro 2016 games were not broadcast in 4K, the TVs had the ability to "upscale" the footage to improve picture quality.
This involves using software to infer what each of the extra pixels should show, rather than just making each square of four pixels the same colour. The technique cannot put back the original detail because it was never included in the lower-resolution broadcast, but algorithms can try to deduce what would have been shown.
The retailer's ad had been submitted to Clearcast - a clearance service for advertisers.
That firm defended its decision to approve the contents on the basis that the TVs had been described as being 4K-ready. This, it explained, implied there was no guarantee that consumers would actually be able to see content in the format.
However, the ASA rejected these responses saying it still felt consumers were likely to have believed they could watch the matches in "genuine 4K definition".
Its verdict followed an earlier ruling against a Currys PC World ad that had said Ultra HD TVs allowed families to watch their "favourite Christmas movies in greater detail".
The firm had again justified its description by pointing to the sets' upscaling abilities.
But the ASA said it believed viewers had been misled to believe they would be able to see the films in "full" 4K quality and added that if the firm meant to refer to upscaling, it should be clearer about the fact.
Currys PC World has been reprimanded for a second time about broadcasting misleading adverts for 4K televisions.