Suddenly on one of my hosted sites I get "Service unavailable" when trying to access the website (Umbraco 4.0.2.1 on MySql db).

I'm also unable to log in to the admin section, when trying to restart Umbraco i get the error below. I wonder if the "Object reference not set..." after umbraco.BusinessLogic.User.getUserId in the stack trace indicates some sort of db issues? I'm able to access the db from VS using ODBC and everything apparently looks ok.

Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]
   umbraco.BusinessLogic.User.getUserId(String lname) +38
   umbraco.BusinessLogic.User..ctor(String Login) +99
   umbraco.providers.UsersMembershipProvider.ValidateUser(String username, String password) +31
   umbraco.cms.presentation.login.Button1_Click(Object sender, EventArgs e) +84
   System.Web.UI.WebControls.Button.OnClick(EventArgs e) +111
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +110
   System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +36
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncP

I tried copying everything (files+db) to another account on the same host, and that seems to be working perfectly.

According to the host everything should be in order - although ...

Any ideas ?

>Tommy