1. Re-install the driver for the printer on the computer for user who is printing checks who is experiencing the issue being sure to use a the most current correct driver from the printer vendor the printer model in question. Windows can automatically find drivers, but sometimes it is best to go directly to the printer vendor's website to get the most recent driver they have published.
2. Make that the user's Windows account has permissions to the folder where the auto signature file is kept on the network.