Do all of your other forms have the paid features enabled? If so, its likely the form you are editing was created by someone with a free account and it was shared with you. The feature level of a form is determined by the author's account.
I figured out what caused this problem for me. A co-worker logged on using her personal account, as she does when viewing forms that were shared with her. She created a form that I was to complete later. She therefore was designated as the "author" of the form and I was the "co-author". She isn't the owner of the FormsCentral account so her form didn't allow the paid features to be accessed. I'm the owner of the account. I was able to get around the problem by duplicating the form which automatically made me the author and gave me access. Interesting. Good to know and share.
Wow. I didn't see your comment and sure enough that's what I discovered. Thanks for your very quick reply to help!