That looks like you may have an older version of one of the Bouncy Castle jar files in your userlib.

To fix this, open up your project’s userlib in Windows Explorer. Look at the modules and look for any with the same name but different version numbers. You want to keep the version with the highest number and remove any others. I would move them to another folder so you can restore them if necessary. Once you’ve done this, try rebuilding your project. It should work.

Good luck, I hope this fixes your problem.