Looks like the "1st" in the date was not accounted for. Attached is the fix.
Extract the attachment somewhere temporarily.
* After that, open up Theocbase and go to Settings.
* Click on "Run Special Command"
* In the dialog box, navigate to the txt file and "open" it.
* Restart Theocbase and you should be able to load the workbooks.
@Jonathas, Juhani asks for the exact error. It would help if you would put the exact error here, either in words or as a printscreen. It would help develop a fix.
It is nice you found a workaround, but in the end we don't want workarounds...