Error: Object reference not set to an instance of an object.

In: at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add) at DotNetNuke.Entities.Users.UserController.GetUserById(Int32 portalId, Int32 userId) at DotNetNuke.Modules.Blog.Templating.LazyLoadingUser.get_User() at DotNetNuke.Modules.Blog.Templating.LazyLoadingUser.GetProperty(String strPropertyName, String strFormat, CultureInfo formatProvider, UserInfo AccessingUser, Scope AccessLevel, Boolean& PropertyNotFound) at DotNetNuke.Modules.Blog.Templating.BaseCustomTokenReplace.replacedTokenValue(String strObjectName, String strPropertyName, String strFormat) at DotNetNuke.Modules.Blog.Templating.BaseTokenReplace.ReplaceTokenMatch(Match m) at System.Text.RegularExpressions.RegexReplacement.Replace(MatchEvaluator evaluator, Regex regex, String input, Int32 count, Int32 startat) at System.Text.RegularExpressions.Regex.Replace(String input, MatchEvaluator evaluator) at DotNetNuke.Modules.Blog.Templating.GenericTokenReplace.ReplaceTokens(String strSourceText) at DotNetNuke.Modules.Blog.Templating.Template.ReplaceContents()