To fix this, you need to log into Dashlane on your computer and then go into 'Tools'. From there, you need to click on 'Preferences' (ctrl+o) and head over to the 'Security' tab. You will need to unlock the settings which can be done at the bottom of the window and will require you to enter your password. Inside 'Security', you will find 'Advanced', head there and then look for the option that says 'Verify browser code signature' and uncheck that. This should fix your issue as it has just worked for me.
See here for more information: https://support.dashlane.com/hc/en-us/articles/360000045799-Autofill-doesn-t-work-on-my-computer
I hope this helps.