I'm trying to create a filter for the Milestones Due that is part of the Project Overview report. I want the filter to only look at milestones due in the next 14 days.

I've created a custom date that is equal to today + 14. It is called 2 Week Look.

When I attempt to use this field as a value in my filter (Finish / Is Less Than Or Equal To / 2 Week Look) I receive an error:

The entry is not valid.
The test value cannot be used with the field for the data you want to find or filter for.

Any help as to why I'm receiving this error and if there's a way to create this filter is greatly appreciated!