Update a field with another field value

[Paul Grimes]

Hello
I am trying what I thought would be a simple task, but I am struggling

I have a table as below

CREATE TABLE `labour` (
`id` mediumint(5) NOT NULL,
`Job_No` int(10) NOT NULL,
`Paying_Rate` double(7,2) NOT NULL DEFAULT '0.00',
`EngineerId` mediumint(7) NOT NULL,
`Working_Hrs` varchar(10) NOT NULL DEFAULT '0',
`InvoiceHours` varchar(10) DEFAULT NULL,
`Sheet_Returned` tinyint(1) NOT NULL DEFAULT '0',
`Invoice` double(7,2) DEFAULT '0.00',
`Send_To_Invoice` tinyint(2) NOT NULL DEFAULT '0',
`Engineer_Note` varchar(200) NOT NULL DEFAULT 'Please Select',
`VAT` decimal(5,2) NOT NULL,
`Total` double(7,2) DEFAULT NULL,
`SubTotal` double(7,2) DEFAULT NULL,
`VATAmount` double(7,2) DEFAULT NULL,
`InvoiceVAT` double(7,2) DEFAULT NULL,
`InvoiceSubtotal` double(7,2) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC;

I want to copy the values form Working_Hrs into InvoiceHours but only if Send_To_Invoice has a 1 as a value.

I have tried various combinations such as this

update `labour`
set `InvoiceHours` = `Working_Hrs`
WHERE `Send_To_Invoice` = '1'
But it is coming back with an error

As I have 79818 to go through, it would be quicker with a query than go into every record, if anybody can please help out?

Thankyou
Paul.