I have installed a web application on a win200 advanced server,with authentication mode=windows and identityimpersonate=true,in IIS(5.1) windows integrated=true,and sql server has sql and windows authentication,it was working on first day,user had entered lots of data,but today i am getting this error..
Either a required impersonation level was not provided, or the provided impersonation level is invalid. (Exception from HRESULT: 0x80070542)

[FileLoadException: Could not load file or assembly 'System.Data, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' or one of its dependencies. Either a required impersonation level was not provided, or the provided impersonation level is invalid. (Exception from HRESULT: 0x80070542)]
NHibernate.Dialect.MsSql2000Dialect..ctor() in c:\net\nhibernate\nhibernate\src\NHibernate\Dialect\MsSql2000Dialect.cs:148



do you suggest some other way of authentication?
thks