It's likely an issue with that station's signal. This sort of problem pops up from time to time with Tivos and is usually resolved after it's brought to the local station's and DirecTV's attention. Have you contacted them?
Sony SAT-T60 120GB (v3.5b)
HR20-700, HR20-100, HR21-200 HD DVR
HR10-250 HD DVR 400GB (v6.4a)
H21-200 HD Receiver
R10 DVR 160GB (v6.4a)