Can't Amplify [SOLVED]

Windows 10 - Audacity 2.1.2 from installer.

This happened in 2.1.1 too, soon after upgrading to Win 10.
I used to be able to amplify, set to not allow clipping, but now the ‘Ok’ button grays out when I try to amplify, even on a thin-line wave that isn’t very loud to start with. I want to amp a couple of dB but no go. Why did it all of a sudden stop letting me amplify?

Perhaps there’s a click at one or other end of the track.

Have you tested the effect on a audio of known amplitude? To do that, generate a tone (“Generate” menu) with the “Amplitude” set at 0.5. Then apply the Amplify effect - it should give you 6.021 dB of amplification. Does that work?

What dB amplification does it default to? Does the default work?

Can you apply negative amplification (attenuation)?

What happens if you allow clipping? If you allow clipping and it works, the clipped parts should be marked in red (as long as Audacity is configured to show clipping). If you run Amplify again it should default to a negative amplification to bring the levels down out of clipping.

…even on a thin-line wave that isn’t very loud to start with.

Peak levels don’t correlate very well with perceived loudness (but the peaks are what clip first if you try to go over 0dB). And like Steve says, it only takes one sample to limit how much you can amplify (without clipping).

Thanks to those great replies I did get it working. Yay! and thanks again.