Q:

Android Studio/Gradle works on 2 Macs. Won't work on 3rd one.

I've been developing on 2 different Macs with latest Android Studio. I just added a separate Git server for version control, and it appears to work with them. 
So I installed Android Studio on a third Mac, and checked out my project from the Git server. The files appear in my local repository, but Gradle reports the following problem and won't let me proceed: 
Error:ch.qos.logback.classic.LoggerContext cannot be cast to org.gradle.internal.logging.slf4j.OutputEventListenerBackedLoggerContext
Possible causes for this unexpected error include:Gradle's dependency cache may be corrupt (this sometimes occurs after a network connection timeout.)
Re-download dependencies and sync project (requires network)The state of a Gradle build process (daemon) may be corrupt. Stopping all Gradle daemons may solve this problem.
Stop Gradle build processes (requires restart)Your project may be using a third-party plugin which is not compatible with the other plugins in the project or the version of Gradle requested by the project.In the case of corrupt Gradle processes, you can also try closing the IDE and then killing all Java processes.
None of the proposed solutions helps. In searching for an answer, I've concluded that the problem may be related to something called slf4j, but I have no idea what this is or what to do about it. 
Why would everything work fine on 2 machines but not on the third? 

A:

I finally discovered that /Library/Java/Extensions contained these 4 .jar files:

logback-classic.jar
logback-core.jar
slf4j-api.jar
xuggle-xuggler.jar

I have no idea how these got there or what they do, but when I moved them out of the folder, the problem went away. 

