There are other ways to create a copy of a project. An alternative is to make a backup of the project using Project Menu > Advanced > Backup Project to File
Save the file to a location on your computer (I create a folder called _Backups in my My Paratext 8/9 Projects folder.
Then restore the file using Paratext Menu > Advanced > Restore Project from File
When you restore you should choose “New Project”. You will need to fill in the basic file information (name and such). You can choose to register, or if this is a secondary version of the main project then you could make it an auxiliary project.
Then you will be able to restore the data. There is an option to restore settings that is by default unchecked since you have created a new project, but you can select this to get some of the other settings (Reference settings, Quotation rules, etc.).
The primary difference between this process and the conversion process is that the conversion process maintains the history. But if you are doing this to simply create a copy then Backup/Restore will work. NO NOT RESTORE OVER THE ORIGINAL PROJECT! This can create conflicts.