I've just stumbled upon this thread... having battled with a warm backup machine for the last couple of days.
I know for certain I haven't changed the password in the advanced section as the new warm backup machine was a clean install onto a new drive 2 days ago, and I didn't even know about the buttons to unhide the readonly fields and make them editable until just now!
I eventually fought my way into mysql command line, dumped the freepbx_settings table to a text file and was able to find the table structure and the field names in that...
Once that was over I was able to just use an sql update to fix it...
Of course once I knew the keyword was call CDRDBPASS, and googled with that, I came straight down onto this page! Typical! Once you know the answer you can find a dozen copies!
So I'm going the throw in some keywords to help others...
Warm backup restore failure.
[1045] Access denied freepbx
Access denied for user 'freepbxuser'@'localhost'
Reload failed because retrieve_conf encountered an error: 1
I've now blanked the password from the advanced settings, but if that doesn't work I think a post-backup sql command script coming on...