The source of the error appears to be clear: using an incorrect data type for some purpose.
Solution: make sure the data is the correct type.
Almost any sort of "automated" data load where the properties of variables are not controlled may eventually lead to such a problem. A common approach it to control how the data is read into SAS for use to ensure appropriate data types and values. Without knowing a LOT more about your data sources that sort of generality is about all that can be provided.
Warning: some file types seem to lend themselves to more data inconsistency issues than others. Spreadsheets do not generally provide any sort of column restrictions so you can end up with some character values mixed in with what should be a numeric column or vice versa. Not much in the way of automation is possible with this if the source is poor to begin with.
