• by David Goetzl  @dgoetzl, Joe Mandese  @mp_joemandese, June 21, 2012

Nielsen continues to evaluate problems that impacted results for the May sweeps period, including errors in the diary printing process, sources said. The misprinting affected how people could properly fill out the documents, which are the sole ratings drivers in 150-plus local markets.

The data collection for the May sweeps was also affected by issues with Nielsen’s call center operations, where employees interact with diary users and look to ensure that they fill out the material properly.

Frustrated station executives have complained to Nielsen and issues were discussed at a Media Rating Council (MRC) meeting on Wednesday. May sweeps data is still coming out, so it may be some time before the full extent of the problems -- such as how many misprinted diaries were distributed -- is known.

Nielsen, however, says it made adjustments in a timely enough fashion so that May sweeps data is sound and station executives can be assured that ratings are reliable. “Nielsen ensures that any data provided to clients meet or exceed the requirements set by the industry for representative results,” the company said in a statement.

The MRC is looking into the matter and its CEO George Ivie said in an email that the organization has asked Nielsen for various data involving the May sweeps.

The MRC revoked accreditation for the Nielsen diary-only measurement service in late 2010, and a Nielsen appeal was turned aside.

Nielsen pins some of the blame on issues encountered while trying to improve the diary system. Areas include communications with households and “upgrading the recruitment calling platform,” the company said.

Wayne Friedman contributed to this story.