Although the window of opportunity to change Medicare drug plans or sign up for a plan ends December 31, some drug plan enrollees may have more time.

In yet another glitch in the problem-plagued program, some drug plans were late in sending their enrollees an official "Notice of Change" outlining planned changes to premiums and covered medications for 2007. If they intended to alter their offerings, drug plans were supposed to send these notices to enrollees by October 31, 2006, so the enrollees could make an informed decision about whether to switch plans for 2007.

For example of the 4.5 million seniors enrolled in United Health Group's plan, some 200,000 got belated notices due to mistakes in the first version printed. Medicare official Jeff Nelligan says the agency does not know how widespread the problem is but that any enrollee who got a notice late will have until February 14 to change plans.

Deene Beebe of the Medicare Rights Center says even seniors who got the notices didn't always understand them.

For a short segment about the glitch aired on the public radio show Marketplace, click here.