SQL Error on adding user

When trying to sync our AD or add a user from our AD i am getting the error message "Error executing sql query. Query" on running the Log viewer it is coming up with the error message:

Application Name : Ensemble2006

Process ID : 48404

Date :18/12/13 10:38:16

Log Level :Error

Log Category :DALProxy

Message : 

[DAL] Error executing sql query. Query

[DAL] INSERT INTO [UserEmailAddress] ([UserEmailAddressID], [UserID], [SendNotificationsHere], [EmailAddress]) VALUES(@UserEmailAddressID, @UserID, @SendNotificationsHere, @EmailAddress)

[DAL] -- error.ToString() --

[DAL] System.Data.SqlClient.SqlException: Violation of UNIQUE KEY constraint 'IX_UserEmailAddress_EmailAddress'. Cannot insert duplicate key in object 'dbo.UserEmailAddress'.

[DAL] The statement has been terminated.

[DAL]    at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection)

[DAL]    at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj)

[DAL]    at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj)

[DAL]    at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString)

[DAL]    at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async)

[DAL]    at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result)

[DAL]    at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult result, String methodName, Boolean sendToPipe)

[DAL]    at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()

[DAL]    at LogicBase.Framework.DataLayer.DALProxy.PrivateExecuteNonQuery(String transactionName, DatabaseQuery query)