eM Client suddenly requires startup password

[sunriseal]

This was posted previously and offers a possible resolution:

How to reset the startup password on eM Client 7 ?

There is a file you can delete, but you will lose most of your settings. You won’t lose any data, nor items like Rules, signatures and templates. Close eM Client, and then delete C:\Users_[username]_\AppData\Roaming\eM Client\settings.dat. You may have to show hidden items in Explorer to do that.