For those of you that receive the message 'You cannot use chat' when trying to use 'Start new chat' here is a walkthrough on how to resolve this problem.
Why this occurs:
This message occurs when you are using a 'Sub Account' which has had chat restrictions applied to it by its 'Master Account'
How to resolve this:
1. Sign-in to the PLAYSTATIONŽNetwork using the 'Master Account'
2. Once signed in go to PLAYSTATIONŽNetwork on the XMB and select [Account Management].
3. Once the page loads select 'Account Management' (Edit your account information)
4. Now choose 'Manage Sub Accounts' here is where you change the settings for your Sub Accounts.
5. Now select 'Parental Control' (View or edit parental control settings)
6. Enter the password when asked.
7. Now you'll have to select the 'Sub Account' you wish to change restrictions for.
8. Now ensure that 'Restrict Chat with Other Users' is set to 'No' then click continue.
9. You should have a message on screen saying that the update was successful, now click continue.
10. Now exit 'Account Management', login to the 'Sub Account' by going to [Users] and choosing the account.
11. Now sign-in this account by going to PLAYSTATIONŽNetwork and select [Sign in]
12. Now go to [Friends] and select (Start New Chat). If it launches, then you have correctly resolved the problem.