There are two major reasons behind the Quicken password not working. These are:
Entering an incorrect password;
Some network issues are hindering the connection.
The most direct way to fix this issue is:
Launch the Quicken file with the data file password, and click Forgot Password;
Choose the option to receive a security code. It can be on the phone or email address. Then click Next;
Enter the code and click on Verify;
Next, choose Open the Data File;
Finally, set the new password by navigating through File > Set Password.