"This intimation is received when you have a tax demand pending from the IT Department and when you have claimed a refund from them in some other Assessment Year.
Section 245 of the Income Tax Act empowers the Assessing Officer to adjust refund (or a part of refund) against any tax demand which is outstanding from the taxpayer.
In simple words, the IT Department wants to adjust your refund due to you against a demand which is due from you. This demand may pertain to an earlier assessment year.