Is this second box a V6? Check here if you're not sure.
If so - I'm going to guess your live TV is ok and this problem only affects OnDemand, and streaming programmes from your other box that's (presumably) downstairs with your router.
Assuming this is the case... the issue sounds like the WiFi signal may not be sufficient in the second location. On the affected box, follow Home > Help & Settings > Settings > Network, and in the top-right the box reports the signal strength. What is reported?
If the signal strength isn't sufficient, then there is one small tweak you may be able to try but your options are inherently limited.
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