Red Notebook displays only squares

Hello everyone,

I have been using Red Notebook for many years and I enjoy the program very much. However, since a couple of months I wasnt able to use it at all. All text is now displayed as squares and I dont know why. I tried reinstalling RN but that didnt help.

My background information:

I am running RN from a USB-Stick using Portable RN (https://portableapps.com/apps/office/rednotebook_portable)
The version I am running is 2.3.
I use Windows 7 with all updated patches.
Other portable apps work just fine.
I dont have that problem with any other program.

Does anyone have an idea what the problem could be? When I click on search items, I can find my entries, so the data seems to be there, but instead of the text... squares only.

I already asked the same question over at the Red Notebooks forum and they asked me to try the non-portable Version of the software. That one works fine, but I would love to get the portable version to work as well. Any ideas?

Thank you for your attention and your dedication to this nice program!