Missing Thumbnails?

I’ve experienced some web site issues of late and I’ve almost got everything back working correctly.

My only real issue now is thumbnails for images in my media gallery aren’t displaying?

If I click on the thumbnail and go into the image the it’s displayed but it won’t display in media gallery – when I got to Smush.It I just keep getting an error and I’m not sure what to do so any help would be appreciated?

All the errors seem to be with image size 340×340, for example – ‘Could not find /home2/gagabibs/public_html/wp-content/uploads/2014/05/colour_cat-340×340.jpg’

I have hundreds of these.

Thanks in advance for any help, I’ll keep looking for answers ??

Regards,
Sean.