We had several customers report problems sending bitcoin to us today from Coinbase. Coinbase was reporting "invalid btc address" for perfectly valid addresses. I'm hoping it's resolved now, but if you see this message while using Coinbase, the problem is on their side. From what I've gathered, this problem was only occurring on their web page; it didn't affect their android and iphone apps. Here's some info about it:
https://www.reddit.com/r/CoinBase/comments/7bzqvk/enter_a_valid_btc_address/