The issue is somewhere in the thumb.php file. This is probably from the TimThumb script.
You can see the actual problem if you go to this link (it should return a thumbnail of the image):
https://kellysrestaurant.com/wp-content/themes/InnovationScience2/thumb.php?src=https://kellysrestaurant.com/wp-content/gallery/catering-gallery/catering0.jpg&w=232&h=112&z=1&q=65
The particular error that is causing the file not to return a proper thumbnail could be a simple whitespace problem (have you edited the file yourself?), meaning there is some extra space in the file where it shouldn’t be. Or, the file might actually do some fancy work with headers, so the problem may be more difficult.
Seeing as it is a well established script, it might be the simple whitespace issue. You could try replacing thumb.php with one downloaded from the project site for a (possibly) simple solution.
Your theme includes NextGen Gallery, but the gallery on the page isn’t actually utilizing NextGen directly (or in a standard way, if it is). Nextgen creates thumbnails for you, and includes those in its gallery directly making it very easy to use. I would suggest you use NextGen Gallery for this page, as it has all sorts of features you might find useful.
Go to NextGen’s “Manage Gallery” page and find the gallery you want to include. Note the ID in first column. Then just include this bit of code on your gallery page, replacing the * with the gallery ID:
[nggallery id=*]
To make it easy, you could just create a new page for this, and just unpublish the non-working page so you have it for the future if you find a fix.
