I recently started using my ereader for cookbooks. The library had lots of them, with no waiting lists. So I checked a number out, opened them with ADE, browsed through them to see what kind of recipes they had and then used the "return book" function in ADE.
I went to check out another book and got an error:
Error code: 710
Error details: Early return error
I emailed support and got the following response:
"We regret to confirm with you this error message is being
> shown because you have returned an excessive number of Adobe
> eBook titles over a short period of time. OverDrive Support
> recommends that you try and check out your Adobe eBook in a week or so.
>
> Should the error message persist, it is recommended
> that you allow one of the books in your account to expire
> and be auto-returned by the system as repeated attempts to
> early-return may cause the system in OverDrive to 'lock' the
> account temporarily.
The problem is, that I had a book that's been on my wait list a long time FINALLY become available and I can't check it out.

If I wait a week, my hold will be canceled and I will go back to the end of the line.
I thought I was doing a good thing by returning the books I didn't want early, so others could access them. Now it seems my account is locked. My next book isn't due for 24 more days, so I have almost a month where I won't be able to check out my holds as they become available.
So be careful with how many books you return early!