Struggling with what seems to be a simple error but weird situation "This entry is invalid"

[iamhitesh89]

I have a very simple dataset with "Term," "Chapter," and "Description." The key and label is selected to be the "Term" column. I'm experiencing the following two issues.

1. I'm not able to edit the existing entries beyond a few limitations, which is shown in the below Photos. The description has to match the previous entry, and if all matches the same, it doesn't allow me to add more characters to it. (Look at the Test 5 entry.)
2. I'm not able to add new entries too. I ensured the table settings are checked ON for updates, adds, deletes. The database is also ensured to be free from formatting. 
3. Existing entryEdit acceptedInvalid entrySettingsSettings

I'm still a noob here. Trying to build a simple data collection (like a dictionary/glossary) for the technical terms that I'm learning in my classes. Any assistance here would be greatly helpful.

Thank you!