After reverting back to html 4.01-strict from xhtml and making the necessary alterations, I ran the page through a validator.
I got 1 error, but a really strange one.
To open links in a new tab, is use the [ target="_blank ] system. There are plenty of these on the page, but only one comes up as an error in the validator. Why?

All the others are exepted, only the first one is not.
All the links work by the way.

[<a href="http://www.boiler-breakdown-repair-london.co.uk/wp" target="_blank"> The Boiler Repair BLOG</a>] error


[ <a href="http://www.boiler-breakdown-repair-london.co.uk/flue-gas-analysers-boiler-repairs-south-east-london-bromley.html" target="_blank"> Flue Gas Analysers</a> ] fine

Only thing I can think of is that all the working links end with either .co.uk or .html
But why would that influence the validator on regcognising the "target" attribute?