Could you give more details about this problem?

Did you use gnotime 2.3.0 before or was this the first time?
Did gnotime crash or just displayed an empty project tree?
Is your data file really empty? (see below how to recover your data and check if its empty)

Recovering your data:

You may be able to recover your data through the backup copies in the ~/gnome2/gnotime.d/ directory.

In this directory, the file gnotime-data.xml is the current data file and gnotime-data.xml.X.Y (where X ans Y are digits) are the backups, being gnotime-data.xml.0.1 the most recent one.

Try copying one of these files to gnotime-data.xml and and then starting gnotime.