The IRS is contacting your because their records indicate there is an outstanding refund check issued to the taxpayer - the refund check is outdated and no longer valid. If you still have the check, destroy it and contact the IRS to receive a new refund check. If the check is lost contact the IRS at the number on the notice to verify your information and receive a new refund check (if you filed a joint return, the IRS will send a copy to each spouse that contains the same information).
Sections of the Notice:
Sample CP 32A: PDF Page 1
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the webpage or document at the time it is accessed.