Sounds like you've got an old TiVo box (check here if you're not sure) and there could be 2 reasons for this...
1: The box's internet connection is failing - on the front-left of the box, there's a series of green lights. Second from left has a heart symbol next to it and is the box's "Online" internet light. It should be solidly on, but does it flash? If so, that's the internet connection failing - anything online will consequently fail, and that's a fault which you need to report via 150.
2: The box is just struggling with the Netflix app - if the online light isn't flashing, then the TiVo - whilst perfectly serviceable - is elderly hardware and can sometimes struggle with newer apps and suchlike. If you have VM broadband and have had your current package for a while, then it would be worth considering a look at newer (potentially cheaper) bundles which could include a box-swap to the V6 box.
It's newer, quicker, has more recording tuners than the TiVo, but handles apps such as Netflix & iPlayer much quicker. Also it has additional apps not available on the TiVo such as ITV Hub, All-4 & Amazon Prime.
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