Hi Diane!
The message you are seeing would be the same as if you uploaded a dataset into Apptio - not via datalink - any validation warnings against the upload will display.
In this case it means the "Tower" column was added to the dataset from the source system, and the time period prior the column did not exist.
You can disable validation in datalink if desired for specific connectors, but I suspect this warning will have no impact in your clients configuration as the new column was most likely unused prior.
Seth