You might try right clicking the desktop and select personalization. Then select the Window Color option at the bottom, then Advanced appearance settings.
In the Item selection box, look for Message Box and see what Font it is using. It should be Segoe UI size 9. There is a possibility the wrong font is being used, and if the program is older, it might be related.
If not that, what screen resolutions are used on the system it seems to work with?