My client's business has new ownership and they want the email address on their paid account to be transferred to someone else. This other person has a free basic account already with FormsCentral, so I'm getting an error message. Is there anyway around this? Or how do I delete the new person's free account in order to transfer the existing account?
The email address that you want to use for the new email address as you've found cannot be tied to an AdobeID. There is a way to make the changes, it requires you having access to a third email address that does not have an AdobeID associated with it.
If you have access to an Email address that doesn't have an AdobeID you would sign into the Free account (the email address you eventually want connected to the Paid account) and follow the steps to change the email address (outlined in this forum thread: http://forums.adobe.com/message/5942171) changing that AdobeID to use the third "un-attached" email address. After you've done that you've "freed up" the Email address you want to connect to your Paid account and you can sign into that account and change the Email address there. Last if you want to you can sign back into that Free account and change the Email address there to be the one you just dis-connected from the Paid account (optional).
PS - I just wrote an FAQ which covers this: http://forums.adobe.com/docs/DOC-4272