Yes exactly, Cathal.
I tried to change the password via Host -> Super User Accounts -> Edit (pencil symbol) at the Host account line and then Manage Profile tab.
Being logged in with the same Host user account, I deactivated the CAPTCHA use, via Admin -> Site Settings -> User Account Settings and in Login Settings sections I unchecked the: Use CAPTCHA to Change Password.
Irrelevant: the Use CAPTCHA to Retrieve Password is also unchecked.
Also, in my web config:
The case is very similar as DNN-4757 JIRA, but not exactly the same.
Should I create a new issue of my own, or just comment on that one (DNN-4757)?
Note again that when I de-activate the CAPTCHA to Change Password option the password is changed with no problem.
I do not know if it's relevant but I'm noticing that I have now 2 series of Host Super User account and this, I presume it may arise from a Parent Portal addition. Please see another issue arose on http://www.dnnsoftware.com/forums/forumid/108/threadid/506621/scope/posts/threadpage/3
I do not know if these two are associated. Just trying to provide as much relevant (or irrelevant for me) information as I can :)
Available to provide any addiitional info to reproduce the error.