Speaking at the release of Granada's interim report, its chief executive, Steve Morrison, said there was "concern about the new Barb audience measurement system".
Barb has been beset with problems and setbacks with the installation of its new panel, which was to have been operational in the new year.
However, there have been numerous delays and observers predict that the end of the year will be a more likely delivery date.
The shareholders - consisting of all the major broadcasters - have consistently rallied around Barb but privately there have been concerns about the quality of the company's data.
Morrison said: "Granada, in common with the broadcasting industry, continues to have concerns about the new Barb audience measurement system. Barb management and industry representatives are addressing the shortfall in the new panel and working to resolve the outstanding problems."
Granada unveiled losses of £169 million, caused by ITV Digital's collapse and reduced ad revenue.
But Morrison has ruled out stepping down, despite speculation that his job is on the line because of Granada's lacklustre performance. Barb's current panel has produced some spectacular results. ITV has suffered, with drops across the majority of its audiences.