Can't change my signature

[Sevenup]

I have decided that I need to change my signature but keep getting the following.

Server Error in '/cs' Application.

---

Cannot

insert the value NULL into column 'UserId', table

'LCommunityServer.dbo.aspnet_Profile'; column does not allow nulls.

INSERT fails. The statement has been terminated.

I can't see anything wrong with what is entered in the page and I have tried Maxthon and Firefox to make the changes.

Does anyone know what can be the problem?