To be sure you are not using the just the comments. Go to System> Change System Settings> Treatment Plan Finaincal Arrangment Notes. It is supposed to take at least 1046 characters.
Also check your form
I am not sure what the problem is but maybe going to the root to add the note or comment may solve the challenge. My screen shot below shows it takes multiple lines for both.
That would be something for support to address ( if you have not already) with the inability to print a form. It could also be on the verion of SoftDent that is being ran. Most issues like that were fixed in newer builds. Either way the goal was to type more then two lines. Did you succeed?
We were able to fix this issue by correcting a corrupted treatment plan form file. Office is now using the form to include both treatment notes and financial notes. While this is not unlimited in the amount of text you can include, it does provide more room for your messages.