We printed a job on C1S (coated one side) stock and the ink on the backside has not dried. We believe the stock is defective. Has anyone else had this problem?

Some paper mills do not recommend printing on the backside of some C1S sheets as they can have a high acid content that interferes with the ink drying. Printers will get away with printing on the uncoated side, and then one variable changes and they have a problem. A paper mill representative once told me, "We didn't coat the backside because we didn't intend for it to be printed on." Check with the mill or your paper merchant to see if it recommends printing on the backside of a specific C1S sheet; there may be other C1S sheets that will dry better.