Allowing Network Access with Blank Passwords

Although you can log in locally without a password, but by default Windows XP does not allow network users to access the computer without a password. 

Typically you will get 'Unknown error 31' or 'Access denied' errors. To override this problem follow the below steps.
Go to Start -> Run and type gpedit.msc and then press enter. 

Wait for the Group Policy Editor,

 go to Computer Configuration -> Windows Settings -> Security Settings -> Local Policies -> Security Options and then double click on Accounts: Limit local account use of blank passwords to console login only and Disable it.