You have posted what is an impossible question - to be able to help context around the error would be required - session logs, solution release, etc. My recommendation is to try recreating your schedule to see if that fixes the issue, if it does not then raise this with the product support team. Hopefully you are upgrading in a controlled way - testing all interfaces and features in a Sandbox environment before rolling out into production, so this should not be an urgent issue. If you have seen this issue for the first time in production I recommend your team revisit how you plan product upgrades in future.
