I would check if you have a Form Personalization causing this and then if so removing/disabling the personalization if it's not needed
With the form in question open go to:
Help>Diagnostics>Custom Code>Off --> This will turn off ALL Personalizations. If you set this and the Note message doesn't appear then there's a personalization causing it
Help>Diagnostics>Custom Code>Personalize --> This will show you all the personalizations for that form.
It must be due to some personalization testing work,as your instance is DEV that means some one has created a personalization for testing.
just go to personalization and check in action tab where the 121 message has been given and just unchecked it.
If you follow Janel's instructions and find that it is a personalization, you can click on the Actions tab and scroll through the personalizations to look for messages that might return just a number; it will probably be a variable name or a sql statement that returns one value. Just wanted to mention that since many people start by reviewing the conditions, which can be complex and take a long time, while going straight to the actions will narrow down the suspects faster.
Also, before turning it off, do a record history and see who created the personalization. Contact that person because he/she may just turn it right back on again to continue working on it. Ask that the personalization be limited to the user himself only, so that he can see his message and you won't (he can do that on the Conditions screen of the personalization form by limiting it to his username or a certain responsibility, etc)