THIS! I actually created this account just to reply to this, because I've been banging my head against the wall all morning before I figured it out, so I figured I should pass on what I discovered.
Here's the issue: for some reason, YOU CAN'T SAVE A CHANNEL TO MEMORY IF YOU ARE CURRENTLY RECEIVING ON THAT FREQUENCY! I don't know why this would be the case, but there it is. I ran into the issue because I was attempting to save a NOAA weather alert station, but I couldn't get the stupid thing to save. Just on a whim, I typed in a different freq (with no one transmitting on it) and it saved just fine. The issue, it turns out, is that because the frequency in question has a weather broadcast station operating on it, my radio was always receiving on that freq, and for some reason Beofengs won't let you save it into your channel memory if that is the case.
So here's the solution: if the frequency is a repeater or some other popular freq, just wait until no one is using it before trying to save. The little green light on your radio indicates you are receiving, so you have to wait until it turns off before you will be able to save. If the frequency is something like a weather broadcast, you will have to get more creative. Go into your basement, or maybe program it inside the trunk of your car. Hold the phone in your microwave while you're saving (I shouldn't have to say this, but please don't turn it on). Basically, find somewhere where your reception is terrible. Alternately, do what I did: unplug your antenna. Obviously you don't want to transmit without an antenna, but if you unscrew it just enough to make you lose reception, you should be able to save the station with no issues. If you're concerned, maybe hook it up to a dummy load, but I don't think you should have any issues as long as you're not transmitting.
TL
R Baofengs can't save a frequency while they're receiving on it, so either wait for everyone to shut up or figure out a way to block your reception.