com.atlassian.confluence.setup.xstream.EnumConverter cannot be cast to com.thoughtworks.xstream.converters.Converter
We don't know the reason why it happens, but in one instance there was an issue while casting the saved theme config.
We created a quick hotfix to solve this issue
March 12, 2015, 8:28 AM
changed implementation to use com.thoughtworks.xstream.converters.enums.EnumConverter