Unable to convert classes into dex format.

Hello Everyone,
I am trying to build an android game where I need to manually access the keyboard so I have written a plugin but when i try to build it gives me an error which says : Unable to convert classes into dex format.
When I visited the forum to resolve this error it says there may be a possibility of two or more jar files but i am sure there is only one jar file in my project, under Plugins/Android but it still throws the same error, How do I proceed?

Hey Thank You Saurabh, I figured it out, It was version compatibility issue.