If it "still works great with your antenna" it sounds like you need to rerun Guided Setup on the TiVo to get the info for the new provider. You cant "hot swap" between the two.
Make sure the card is activated!
TiVo Premiere Elite
TiVo Mini TCDA92000 (Codename: UNICORN)
TiVo HDXL TCD658000
TiVo HD TCD652160 + WD 500GB Expander
Retired: Philips Series 1 HDR212 & TiVo Series 2 540080