Try the following:
- Launch TopAccess
- Select Administration and log-in
- Select Network under Setup
- Select the SMB Session
- Set "SMB Signing of SMB Server" to "If client agrees, digital signature is done for communication."
- Select Save for the SMB Session
- Select Save for the Network Setup (the MFP will Reboot)
As for the message, just use the slit-glass cleaner located in the front cover and the message will clear on its own.