The validator errors for the grid_lightbox template are for 4 things:
1. Links to stylesheets are within BODY tags instead of HEAD tags.
2. The thumbnail IMG has two ALT parameters; alt="" and alt="test"
3. HTML is used (strong) within the value of the NAME parameter on the A tag for the thumbnail.
4. The A tag for the thumbnail uses NAME for image title and description, but the validator says that NAME should be one word (token).
Since I am displaying the PowerGallery within a page, I put the PowerGallery stylesheet links in the HEAD. I changed the galleries\grid_lightbox\index.php and moved the stylesheet links to before the closing IF for when PG displays the complete page. That solved #1.
For #2 I edited the same file and removed alt="test" and set a value in alt="" (the name of my website).
For #3 I edited the same file and removed the <strong> </strong> in the NAME parameter on the A tag for the thumbnail.
These changes brings the page down to 1 error for each thumbnail - the use of NAME to hold image title and description. I assume the TITLE parameter on the IMG tag is used to display the tooltip and NAME on the A tag is used to display title and description in the lightbox image? Can I make changes to PowerGallery files to use a TITLE parameter on the A tag instead of NAME?
There is also one warning which I don't understand:
Byte-Order Mark found in UTF-8 File
check?uri=http%3A%2F%2Fwww.archaeology-travel.com%2Fsite-photos%2Fengland%2Fsouth-west%2Fgreat-witcombe-roman-villa%2F279%2F&charset=%28detect+automatically%29&doctype=Inline&group=0&user-agent=W3C_Validator%2F1.2
