FYI – This problem was solved via email.
If anyone encounters a similar issue, solving it typically involves removing the saved application state.
1 – Open the Finder
2 – Select Go > Go to Folder (OR Shift-Command-G)
3 – Enter ~/Library/Saved Application State/com.visualdatatools.datagraph.savedState/
Note: By default, this is a hidden folder.
4 – Remove all the contents of that folder. In fact, you can just delete the entire folder to be sure. It will auto-generate the next time you open DataGraph.
On the macApp store, the folder is in:
~/Library/Containers/DataGraph/Data/Library/Saved Application State/com.visualdatatools.datagraph.savedState/
Once this folder is gone, DataGraph should open normally. If you continue to have problems, email help at visualdatatools.com.