In 4D Server version 6.0.6, if you've selected the "Mandatory Log File" option, but don't own 4D backup, you'll end up in a loop where you're told you can't start the database unless you create a log file, and there's no way for you to create this log file.
To fix this problem, from 4D Server, when selecting the database to open, hold down the Alt key so you get a dialog where you can select the data file. Use the "New" button in that dialog to create a new data file. On the dialog to choose the log file click on the New button. Create a new log file. Give that a different name than the default suggested name. 4D will open your database. Go to the Preferences in the Design Environment and uncheck the "Mandatory Log File" check box.