I have upgraded a site to v6.2.6 from v4, but now I constantly see this error in the logs?

Error executing query delete from umbracoLog where datestamp < @oldestPermittedLogEntry and logHeader in ('open','system')

Any idea how to resolve this? ... Whole error log below

Error executing query delete from umbracoLog where datestamp < @oldestPermittedLogEntry and logHeader in ('open','system')
System.Data.SqlClient.SqlException (0x80131904): The conversion of a nvarchar data type to a datetime data type resulted in an out-of-range value.
The statement has been terminated.
   at System.Data.SqlClient.SqlConnection.OnError(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.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString, Boolean isInternal, Boolean forDescribeParameterEncryption)
   at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async, Int32 timeout, Task& task, Boolean asyncWrite, Boolean inRetry, SqlDataReader ds, Boolean describeParameterEncryptionRequest)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean& usedCache, Boolean asyncWrite, Boolean inRetry)
   at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(TaskCompletionSource`1 completion, String methodName, Boolean sendToPipe, Int32 timeout, Boolean& usedCache, Boolean asyncWrite, Boolean inRetry)
   at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()
   at Microsoft.ApplicationBlocks.Data.SqlHelper.ExecuteNonQuery(SqlConnection connection, CommandType commandType, String commandText, SqlParameter[] commandParameters)
   at Microsoft.ApplicationBlocks.Data.SqlHelper.ExecuteNonQuery(String connectionString, CommandType commandType, String commandText, SqlParameter[] commandParameters)
   at umbraco.DataLayer.SqlHelper`1.ExecuteNonQuery(String commandText, IParameter[] parameters)
ClientConnectionId:820b14ee-77db-4586-baba-e3d5b8472f74
Error Number:242,State:3,Class:16