I Have the same problem, Emailed Lexmark who replied with what appeared to me,(basic knowledge only)to be a complicated solution. it also required the printers IP address,but the details on how to obtain it were given for a different Lexmark model.Whilst trying to find the IP address in settigs,I opened the All in One centre,and much to my amazement, when I clicked on scan it worked,and has worked since.Yet when I press the scan button on the printer it still reads can not download application list.
I think it is worth a try.If you want Lexmarks solution I enclose it below
Thank you for contacting Lexmark International.
Please follow the steps given below:
1. Open your Internet browser application.
2. In the web address field, enter the printer's IP address.
Next to http://, enter , where is the address located on the Network Settings sheet.
11. Once the file has been downloaded, log off the Internet and close all programs.
12. Close the Lexmark Imaging Studio from system tray ( To do this right click on Lexmark Imaging Studio which is on the bottom right hand corner of the computer screen (System Tray) and Left click on exit)
13. Double-click on 3500-4500.exe and run it. You will first see a Lexmark License Agreement and click on 'I agree' and follow the on-screen instructions...
(NOTE: If you are using windows vista, right click on 3500-4500.exe and click on run as administrator)
14. Double-click on 3500-4500wifiethernetpatch.exe and run it. You will first see a Lexmark License Agreement and click on 'I agree' and follow the on-screen instructions...
(NOTE: If you are using windows vista, right click on 3500-4500wifiethernetpatch.exe and click on run as administrator)
15. Restart both computer and printer.
16. Wait for some time till you see the wifi light turning green.
17. Try printing wirelessly
18. Try scanning wirelessly.
Please provide the information listed below to facilitate the record of your case.
Printer Model(Machine type number):
Please let us know the results as we can assist you further.
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If you have any further questions, please reply to this email in the usual way or contact us at our Technical Support Centre on the number above.
Best regards, Madhusudhan Lexmark Technical Support Team