I'll be adding to this list as and when new questions come in.
If you get an error when trying to workflow or save an item that is similar to:
Item validation errors detected:
Field Display Name: Content Start Date
Field Submit Name: sys_contentstartdate
Error Message: at least one value expected
Please go back to the Rhythmyx content administrator and make necessary corrections.
it means that there is no content start date set.
The content start date is the date that the content item will be published out for the first time. Generally it will be the same as the date it was created unless it needs to be published out at a specific date in the future. It gets automatically set.
If it isn't set and you get this error you need to find the 'Content Start Date' and set it, you do this by clicking on the calendar button and selecting the date required.
Please note that the Content Start Date is a different field to the Event Start Date (in event items) or the Press Release Date (for new/press release items).