All the photos that won't enlarge are coded to be looked for in a directory named Photos To Edit.
Do you have such a directory in your source page of coding? I suspect not.
The photos that do enlarge appear to be saved directly in your source code.
Although not usual, for consistency I suggest you save ALL the photos in the source and code them as those that do work (in other words knock out the ../Photos%20To%20Edit/ ). BUT the rogue photos must be saved in the same place as those that work.
Example of one that works:
<a href="Wood%20Pigeon.jpg"><img border="2" src="Wood%20Pigeon_small.jpg" xthumbnail-orig-image="Wood Pigeon.jpg" width="100" height="74"></a>
<span lang="EN-GB" style="font-size: 12.0pt; font-family: Times New Roman">Wood
pigeon.
Example of one that does not work:
<a href= " . . / Photos%20To%20Edit/Danby%20Gull%20Colony..JPG">
<img border="2" src="Danby%20Gull%20Colony._small.JPG" xthumbnail-orig-image="../Photos To Edit/Danby Gull Colony..JPG"></a>
Black Headed Gull Colony.</span>
Not sure why there are two dots in Danby Gull Colony..JPG