In the event that you want to add or disable the comments popping up from invoices, inventories or purchase orders such as this one:

All you need to do is  review whether a feature in the Setup Wizard is on or not.

Step 1. Go to Menu > Setup Tools > Setup Wizard 

Step 2. Go to Inventory > Options 3, and enable Use Inventory, Customer, Purchase, and Unit Warning Comments

Alternatively, if you don't want comments to pop-up from your transactions and inventories, you can just leave it as disabled. 

If you need further help with your issue, please contact customer support at 1-800-663-5750.