Make sure there isn’t any spaces in it. I’ve seen spaces cause issues. Shoot for 10 characters and see what you get. 

I’m having the exact same problem with my TG3452A.  The thing is, if you press the ‘Show’ button on the new password it will tell you if it’s invalid ( missing a symbol, number or too short ) but will still give you the “Bad Password!” pop-up when trying to save the change.

UI with invalid password:

UI with valid password:

Both result in the “Bad Password” pop-up.

Hello,

i have the same problem.

Any solution yet?

Best regards.

Yeah, same issue here. :( 
I’ve got a dg3450

I found solution.

You can change password via Wizard page under Gateway section

@plemans 

No, there is no any spaces.

Had the same situation for modem Arris TG3453 [Internet Service Provide (ISP) is Cogeco in Ontario, Canada]. For some reason it would not accept the administrator password via “User Accounts” tab but it would accept it via the Wizard found under the Gateway tab.

https://support.cogeco.ca/hc/en-ca/articles/4412576607895-How-do-I-set-up-my-ARRIS-TG3452-modem

Same situation here in southern Ontario, with a newly installed ARRIS TG3452 (COGECO ISP). Unfortunately the WIZARD utility has now been removed from the GATEWAY tab. I’ve tried resolving via Tech Support but got nowhere—hence the reason for locating this site.

Incidentally, I just found out that FULL BRIDGED mode in the TG3452 can only be attained by the ISP—the end-user can only configure the ARRIS TG3452 modem to PARTIAL BRIDGED mode. For FULL BRIDGED mode, a request must be made to the ISP, and they will do it online.