I just wasted an hour of my time tracking down a problem with customer support that could've easily been avoided.
A personal plan allows file request folders, which is wonderful. However, deadlines are not supported on personal plans. I kept getting the same error from Dropbox when I would go to submit a request that said that "file requests are not permitted on your personal plan". This is not what is mentioned in the advertised plan, so I assumed there must be an error.
It turns out that the error was that deadlines are not supported for file requests in the personal plan. This is not mentioned anywhere in the literature I could find on the website, and was not mentioned in the error message I got. Once I stopped trying to use the deadline feature everything started working again.
My suggestion: If this annoying little feature is meant to be an up-sell item, it had the opposite effect in my case. I would rather Dropbox was upfront about this limitation in the terms of the plan, or, have a disclaimer about the limitation in the user interface so that one would know that deadlines are not supported--or, better yet, disable the feature completely (grayed out) unless the user is on a business plan.
I wish I could bill Dropbox for the hour of work I just lost tracking down this totally unfair and insipid issue.