Your issue is undoubtedly that the one or more of the JMP columns you are attempting to copy into are numeric, and the data you are attemping to paste into that column are not numeric in form, or at least JMP does not think it is. Without seeing an example of the data in question, I can only guess at a solution.
Many times, if you are attempting to paste in a Time or Date value, and you can have a conflict if in Excel, the values are in a text string, and in JMP you have them in a numeric Date/Time structure. You can fix this copy/paste issue, by changing the "Informat" in JMP to expect the data in the text format specified in Excel.
If the data are invalid-to-JMP values, you will have to copy them into a new data table, then change the column data types, and then either do a concatinate or an Update to put the data together.
Jim