Edit: updated to include the broken release numbers & date range
The Web Audio API was introduced by Chrome in 2011. At the time it was a sorely needed improvement to audio playback in HTML5 games, so we started supporting it in Construct 2.
The specification subsequently was changed and some method names changed. We later updated Construct 2 to match the latest specification.
We are trying to make Google aware of this and have notified them in Chromium bug 396075. Please star the issue and add a comment if it affects you to raise awareness. I am hopeful Google can add back the old names for backwards compatibility.
In case they don't you will need to re-publish all old content using the latest version of Construct 2. This includes games on the Scirra Arcade. The latest stable release is r173. Note that you will also benefit from all the performance and compatibility improvements we've made since then, but there may be breaking changes as well. You can find a summary of all breaking changes by reviewing the release notes for every stable release going back to the time you exported.
The affected versions are between:
Construct 2 r66, released November 7th 2011 (introduced the Web Audio API)
Construct 2 r121, released March 5th 2013 (updated to new method names)
So if you exported your project using any version between r66 and r121, it is probably now broken and needs re-publishing. Note this includes all versions through 2012. If you exported your project using r121 or newer - basically any time in the past year - you will not be affected.
If in doubt re-publish anyway to ensure your games keep working and keep an eye on bug 396075 for updates from Google.