I remember now I handled this issue in the past. This is the "quick and dirty way".
Go to the Description column in the first row of your Excel spreadsheet. Press F2 (Edit) ==> go to the end of data in cell and then enter enough spaces to make the field large enough so that Crystal Reports will recognize this as a Memo field. (This padding with spaces is just temporary). Save the spreadsheet and open Crystal Reports. Open and expand the Explorer pane in CR. If you do not see the field types (string, number, Memo) after your field names, then right click on "Database Fields" at the top of the Explorer pane and select "Show Field Type". The field type should now say "Memo" after the Description field (you may need to refresh your data and/or go to Database ==>Verify Database.
If you still the field type as String after the Description field then "save" the report and repeat the steps outlined above. Once you get CR to recognize the Description as a Memo field and are successful in running your report then save the report and go back into your Excel spreadsheet and remove the padded spaces in the Description field in Row 1 of your data.
I will try to find the Microsoft explanation for this in my files.
Let me know if this works for you.