I loaded the gallery today after users complained they could not upload pictures.
I have now tried rerunning the setup files again and now we are getting the follow error when we try and upload a picture "Fatal error: Invalid image instantiation: file does not exist in /home/harry/public_html/et/gallery/zp-core/class-image.php on line 130"
When we try and create a new album to upload in to we get "Fatal error: Invalid album instantiation: johndory/testing does not exist. in /home/harry/public_html/et/gallery/zp-core/class-album.php on line 653" testing being the new album to create.

Please post the full stack trace from the debug log. And see if there are other errors from the same time. You might have severe file/folder permission issues on your site.

the last entry in the debug.log is dated {32597:Tue, 30 Apr 2013 04:17:30 GMT} so there is nothing useful in it.
I can delete what is there and try the actions again to see if it creates anything in it ?

That would be helpful. Also perform a database refresh that matches the filesystem (the gallery) with the db entries. Such errors can also result from a mismatch.

Tried that, didn't help.
There are now no entries in the debug.log.
Here's a new one I've not seen before but its most likely related.
I uploaded a picture via ftp, no thumbnail has been created for it but you can see the final picture in the album. I then went through the admin menu to edit an album and tried deleting the picture, it claimed to have successfully deleted the picture but it hasn't.

It strikes me it may be easier to back it all up, which it is anyway and bin it and start again with a new install of v1.4.4.8 ?

This all sounds like a file/folder permission issue. You might need to set them manually via ftp then. See the user guide about which are needed.

okey dokey

Ok sorted.
Had to reapply all the permissions by hand then rerun the setup files, then change the permissions again.
Then rerun and setup couldn't open the cfg file as permissions where to strict, changed them from 600 to 644, ran again and it ran as it should, the only thing it couldn't do was delete the setup files, did that by hand.
Thumbnails now being created and everyone can upload and delete pictures now.