Congress couldn't reach agreement on legislation extending the 2001 tax cuts until December, and the IRS couldn't reprogram its computers for the changes in the December compromise until mid-February.  The Service was unable to process federal tax returns with itemized deductions and other items affected by the legislation until February 14, 2011.

Once the IRS started to process returns, they asked processors to limit the number of returns submitted while they catch up.    Even so, the IRS continues to have problems with the system which may delay refund checks.