after updating my qnap to the latest firmware version, i am unable to login with my normal user account. this is the error message i am receiving qnap your login credentials are incorrect or your account is no longer valid
Please check your NAS model, this does not exist (It’s probably the name and not the model)
Here is the default password to whatever firmware you are running (‘latest’ is bogus)
I can’t login using admin.
Is there a known bug with the update that could have caused this?
My Model is TS-453D
No. Please read the help article @dolbyman posted. 
Please first try to log in using the ‘admin’ account.
If you are unable to log in, please follow these steps to reset the admin password:
How do I reset the administrator password of my NAS? | QNAP
After the reset, the default password will be:
What is the default system administrator password for my NAS? | QNAP