Hi,
I don't know what OS you're running but I had the same problem under XP Home Edition after installing SP3. I right-clicked on the ATI TV shortcut, chose Compatibility Mode and chose Win 98/Me. This fixed the problem for me. Hope it fixes it for you.
One more thing: I got this to work in Windows Vista Home Premium by downloading and installing the Windows Vista 32 bit drivers from ATI. They are the ones for the 550 PCI under TV Tuners. I just installed them, installed
ONLY MMC 9.16. The first time you go into TV, if you want to resize the screen, do it manually, or you will get a BAD_POOL_CALLER error that will shutdown Vista.
Don't use compatibility mode with Vista, just install as Administrator.
Right-clock and choose Run as Administrator. I also have User Account Control turned OFF in Vista. I hate the prompts. Everything worked fine as long as I just resized the screen manually by dragging. You may have to reposition your screen 2 or 3 times to make it stick, but it eventually will . . .
Let me know if this helps anyone. Please post replies.
Mark