Cannot edit some imported contact notes

I am impressed how Zoho was able to import gmail contact data via csv, but I am unable to edit some of them in random testing. For example account Bingo, I cannot select Edit and then without changing anything, select Save. I get an error Enter a valid Notes. There is a lengthy note in the Bingo contact, and some words are red underlined indicating spellcheck fail. I shortened the note and deleted the words with red underling to no avail. Still same error "Enter a valid Notes". The error goes away and I am able to Save only if I delete the Note on the culprit contacts. Any ideas? Thank you in advance for any help you can provide.