Please help:

I get an invalidOperationException after I added the Page_Load statement:
ENTUserAccount userAccount = db.ENTUserAccounts.Single(ua => ua.WindowsAccountName == @"VARALLO1\VaralloMadison");


System.InvalidOperationException was unhandled by user code
Message="Sequence contains no elements"
Source="System.Data.Linq"
StackTrace:
at System.Data.Linq.SqlClient.SqlProvider.Execute(Exp ression query, QueryInfo queryInfo, IObjectReaderFactory factory, Object[] parentArgs, Object[] userArgs, ICompiledSubQuery[] subQueries, Object lastResult)
at System.Data.Linq.SqlClient.SqlProvider.ExecuteAll( Expression query, QueryInfo[] queryInfos, IObjectReaderFactory factory, Object[] userArguments, ICompiledSubQuery[] subQueries)
at System.Data.Linq.SqlClient.SqlProvider.System.Data .Linq.Provider.IProvider.Execute(Expression query)
at System.Data.Linq.Table`1.System.Linq.IQueryProvide r.Execute[TResult](Expression expression)
at System.Linq.Queryable.Single[TSource](IQueryable`1 source, Expression`1 predicate)
at _Default.Page_Load(Object sender, EventArgs e) in c:\Documents and Settings\Administrator\My Documents\Visual Studio 2008\Projects\PaidTimeOffSolution\PaidTimeOffUI\De fault.aspx.cs:line 21
at System.Web.Util.CalliHelper.EventArgFunctionCaller (IntPtr fp, Object o, Object t, EventArgs e)
at System.Web.Util.CalliEventHandlerDelegateProxy.Cal lback(Object sender, EventArgs e)
at System.Web.UI.Control.OnLoad(EventArgs e)
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
InnerException:

I loaded chapter 12 code to my solution and get this same error.
No idea where to look next to fix it

I'm an idiot - error means no entry found. Looked at DB and found varralo1\varralom instead of ..varralomadison.