"DotNetNuke.Services.Exceptions.ModuleLoadException: Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression. ---> System.Data.SqlClient.SqlException: Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression. at System.Data.SqlClient.SqlConnection. (SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction) at System.Data.SqlClient.SqlInternalConnection. (SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction) at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose) at System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady) at System.Data.SqlClient.SqlDataReader.TryHasMoreRows(Boolean& moreRows) at System.Data.SqlClient.SqlDataReader.TryReadInternal(Boolean setTimeout, Boolean& more) at System.Data.SqlClient.SqlDataReader.Read() at System.Data.SqlClient.SqlCommand.CompleteExecuteScalar(SqlDataReader ds, Boolean returnSqlValue) at System.Data.SqlClient.SqlCommand.ExecuteScalar() at PetaPoco.Database.ExecuteScalar[T](String sql, Object[] args) at DotNetNuke.Data.PetaPoco.PetaPocoHelper.ExecuteScalar[T](String connectionString, CommandType type, Int32 timeout, String sql, Object[] args) at DotNetNuke.Data.SqlDataProvider.ExecuteScalar[T](String procedureName, Object[] commandParameters) at DotNetNuke.Data.DataProvider.GetDuplicateEmailCount(Int32 portalId) at DotNetNuke.Entities.Users.UserController.GetDuplicateEmailCount() at DesktopModules.Admin.Portals.SiteSettings.UpdatePortal(Object sender, EventArgs e) --- End of inner exception stack trace ---"

Can some one please explain this error and suggest how I might resolve it?

DNN 7.4.1

Thank you for your response Sebastian, but actually what I'm trying to do is make a change under the 'User Account Settings' tab in admin > site settings.

Specifically, I'm trying to enable captcha on the registration form but I check the appropriate box (I've tested this, doesn't matter what setting I try to alter), click update and this error message appears and the change does not get saved.