Hi Tessak,
We apologize for the delay in response.
If you are still experiencing the same problem and looking for the resolution then you may check the following-
1- The email address you have changed to, are you able to Sign In using that email on Adobe.com Adobe: Creative, marketing and document management solutions
2- Logout from the application correctly and log In using the updated email.
3- Go to the Document Cloud website https://cloud.acrobat.com/sendforsignature > Sign In >and try "Send for Signature"
Let us know if anything helps!
Regards,
Akanchha