Error opening /.urbackup_tokens.properties in Version 1.5 on Debian

This problem is known to the developer, and is probably already solved in the to-be-released 1.5 beta.
The version you are using is a very old experimental release; you should use 1.4.10 server instead. If you want to use 1.5, you should wait until the beta comes out.
Further infos: