The first request was blamed on generator outages related to the cold weather. Today's request is also blamed on generation shortages, however, it has (so far) been limited to just two utilities in Maryland, Baltimore Gas & Electric (BGE) and Potomac Electric Power Company (PEPCO).
Interestingly enough, Maryland's electric consumption exceeds its native generation capacity. The U.S. Dept. of Energy's Energy Information Administration reports:
The state's electricity consumption exceeds its net generation, and currently more than one-third of power consumed in Maryland comes from the PJM grid.
But, don't blame Maryland. The state tried to encourage the development of new in-state generation last year, only to have its plan attacked by PJM, the Market Monitor, and the out-of-state generators who supply expensive electricity to Marylanders, and eventually the plan was slapped down in federal court.
Good work, PJM!