Full error message when trying to save the plan:
An unexpected error occurred. Please report this problem to your system administrator with the following information: System.Security.SecurityException: The source was not found, but some or all the event logs could not be searched. To create the source, you need permission to read all event logs to make sure that the new source name is unique. Inaccessible logs: Security.
Please restart the SQL server database instance from SQL server management studio. If this does not resolve the issue, the problem is caused by the fact that there is a collision due to some task dependencies that make planning these tasks impossible. The functionality has been enhanced in Orchestrate version 7.66. Please upgrade to this version. If you are not in a position to upgrade, please raise a new case online and reference the title of this article.