Please upgrade the MailChimp library to version 1.0.9 when upgrading to this version of the MailChimp module.
This release requires a patch. Please apply the patch in comment #10 of this issue.
Changes since 7.x-4.9:
Visit update.php / clear cache. Lots of cleanup and refactoring.
Bug fixes:
Changes since 8.x-1.0-beta2:
Fixes a bug with install hook. Hopefully, no more issues with updates from here on in.