Hi everybody!
I was transferring data and realized it got stuck so I refresh the page. I ve got kicked out of the system (TS-433 // QTS 5.2.9) and now I cannot access as ADMIN. it say ¨Your login credentials are incorrect or your account is no longer valid¨. Same with my personal account but another user can access.
I have tried to recover ADMIN password and it says ¨The email notification settings is currently disabled. Please contact the system administrator for assistance.¨
But I am the system admin…. what to do?
It could be a bunch of things, like the firewall (which you shouldn’t really need) or repeated authentication requests (mapped drive, etc).
You can always do a 3 second reset to clear the firewall and reset to basic networking settings. Read the link to see what is cleared so you know what you may want to re-enable later on.
https://www.qnap.com/en/how-to/faq/article/how-can-i-reset-my-nas
The new default admin password will be dependant on your firmware version.
https://www.qnap.com/en/how-to/faq/article/what-is-the-default-system-administrator-password-for-my-nas
It is possible that it will also clear up by itself after a period of time, if it just locked you out due to multiple authentication failures due to your refresh.
In the future, it would be helpful to include basic information such as your NAS model and specific firmware version. This would help people give you a precise response, where it may or may not make a difference. 
You may also want to try resetting the Windows Credential Manager. Additionally, if you are using the default admin account, we recommend disabling it unless you are sure your NAS is not exposed to the internet, as the admin account is more vulnerable to brute-force attacks.
Hi! nope, I wasn´t using a default ADMIN account. The system has been working properly till now. As mentioned, the data upload got stuck so I refresh it, got kicked out and when trying to login again the password won´t work. I also tried with my personal account but nothing worked. My colleague though managed to enter without issue with their own personal account. I am puzzled.
Not the firewall
Not repeated authentication requests (I was in when I have got kicked out and then could not access)
This is exactly what leads me to it being a firewall / access rules issue. If you don’t have another admin level account to see / clear the issue, then use the method linked above to reset the security and networking.
Please open a support ticket and our Support Team will be happy to assist you further!
Also, may we ask if your SMB transfer is working normally? Is the issue only with logging in via the Web UI?