Welcome to the forum Bobby.
When you've got serial numbers that contain letters, and you want to use the Verify feature (always a good idea), then you'll need to make the field a Character field type instead of numeric. Then you'll be able to Verify without that message appearing.
But if you don't want or need the letters for some reason, then Monarch can strip them out for you by adding a calculated field in the Table window, and employing one of the built-in functions.
I made the changes and the numbers are now showing up in my table. HOWEVER, now i've noticed that the template is referencing the serial number above it instead of below. I have a screenshot to help explain. I just don't know how to get it to you. Shoot me an email and I can send it.
If you have two templates, one of them is most likely a Detail template and the other is an Append template. Try changing the Append template to a Footer template and see if that fixes it. There's a lot of threads here on the forum about this that will go into more detail.