Christina Aguilera called off a concert in Virginia Beach, Va., Monday, just days after canceling a scheduled Boston performance. She is blaming a strained voice and saying that she must stay in bed, reports Reuters. "Due to efforts to avoid a lengthy or serious vocal problem, Christina's doctors, concerned that her voice is slightly strained due to her heavy schedule, have asked her to take three days off and rest," reads a statement on her Web site, which promises that Aguilera will "give a 200% performance!" when she resumes her tour schedule in Camden, N.J., on Friday. There are also reports that she will appear, as planned, on tonight's Latin Grammy Awards. Last week, she performed a memorable high-voltage duet with Limp Bizkit singer Fred Durst at the MTV Music Video Awards.