Printer Always Says Offline

I had the same problem, and couldn't find a solution anywhere. My laptop said the wifi Brother MFC-255CW printer was offline, when the printer was definitely online and connected.
In the end I simply went into Control Panel / Printers, selected the Brother printer, and deleted it off the network.  Then I chose "Add a Printer" from the network, and reselected the only printer on my home network - which was the Brother MFC-255CW that I had just deleted.  The computer reinstalled the driver, and everything was fine again -  haven't had a problem since.

From Brother website/help

1. 1. 1. Click the Add Port... button.
      2. Select the Standard TCP/IP Port option and click
         New Port. The
         Welcome to the Add Standard TCP/IP
         Printer Wizard appears.
      3. Click Next.
      4. In the Printer Name or IP address area enter the node name
         of the
         Brother device as it is printed on the network configuration page.
         An
         example node name could be: "BRN_34FDAA".
      5. As you enter the node name, the Port Name box will be
         automatically updated.
      6. Click the Next button.
      7. Click the Finish button.
      8. Click the Close button on the original Printer Ports
         screen.
      9. Click the Close button to return to the original properties
         screen.
      10. Click the Apply button and then the OK
          button.
      11. Now try to print a test page.
2. This worked great for me!
   

turn off SNMP in printer properties