Can you post the entire error log?
There were no changes recently on the server that would affect this, however if you haven't built in a long time there are some things that could have changed. If you'd like to find out where the change was introduced, I'd suggest pinpointing the plugin through elimination.
If you'd like to just fix it, this should do it:
<preference name="android-build-tool" value="gradle" />
I have several apps that I use PGB to build (paid account). I haven't changed my code and recently, I also get this error. Obviously something DID change. I guess the term "recently" is subjective.
We are SOOO tired of dealing with PGB. We have experienced lots of stability issues. Now we are having to "Fix" our code/config files because PGB keeps changes things up.
To that end, my company has decided to commit full time resources into rewriting our apps...specifically to get off the PGB platform.
Unfortunately yes we do often have to make changes on the server side in order to ensure compatibility with the latest versions of android, and to use the latest sdks. While this will be a "fix" for many, it may cause breaking changes to others. This is the nature of the Cordova / Mobile / Android / iOS platform.
If you're migrating away from PGB you should be able to move to a local PhoneGap / Cordova CLI environment without rewriting your code base, and have more control over your build environment.