The ESignature tab suddenly being grayed out is often due to a standing invoice or an attached credit card on the store.
The two things to check when this happens are:
1. Are there any open invoices on store.officetools.com? You will need to log in as the primary contact where your original order was assigned.
2. Is the card on file active and up to date? It is recommended to re-enter the card information just to be certain.
Once you make any changes, close and relaunch OfficeTools