Many thanks DrByte,
it turned out not to be any of your suggestions above ...HOWEVER.... your suggestions set me to digging deeper into other templates so I did a comparison of tpl_header.php and BINGO !!
The culprit was that the tpl_header.php was a version 1.5.1 on a site that is 1.5.5f ........ absolutely no idea how that version of template ended up on a site that is a newer build than the comparison site, also 1.5.5f and the same template file set was used. Anyway, simply replacing that file with the 1.5.5 version fixed the issue.
Thanks for responding as quickly as you did.
cheers,
Mike
p.s. will look at reverting to .png or .jpg images - was trying to reduce page loading speed
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