Starting on July 1, 2013, for non-competing continuation grant awards, NIH will delay processing if publications arising from it are not in compliance with the NIH Public Access Policy. Articles resulting from NIH funding that have been published since April 2008 must be in PMC to be compliant.
If you find that you have non-compliant citations, you will need to submit them to PMC. There are four different submission methods. The method you use will depend on the journal/publisher associated with each citation.
The NIH Public Access website offers overviews of the policy and the recent changes, along with help documents.