We've re-developed the plugin.
A new version will early June, possibly by the 2nd even. It has a more advanced interface and core. Preparation has been done for WordPress 3.6 which I think may already be overdue for release.
It will not be backwards compatible due to it's low rate of use, this is due to it not being updated or promoted for over 2 years. The other reason is that the old system is so different from the new that migrating the old data is not possible at this time. However it may be possible in the near future when we expand the plugin a bit.
If this is a problem and you are a keen user of YouTube Sidebar please contact us so we can revise the situation.
The plugin is part of our initiative to create a plugin range. We want to work with you and hear from you. If you need YouTube in your sidebar, tell us more. Let us know the sort of tools you vision and functionality that would suit your website.