I refer to this very old post: http://drupal.org/node/313854

I seem to be having the exact same problem.

The entire site breaks with a fatal error "Error. The website encountered an unexpected error. Please try again later." when I add a new image field to a content type. It doesn't matter which content type it is, if I add the image field who site is down!

This has only just started happening. I have previously been able to add a new image field no problems. I have not upgraded / migrated or changed anything. This just suddenly started happening today. When I create a new image field the whole site goes down. If I delete the new field I just created whole site comes back again. Problem is I NEED to be able to create new image fields - this is essential.
Therefore this issue makes the entire site unusable as we cannot add new content.

Un-installing and re-installing the image module is not an option as it is a very large site with a great deal of image content on there. The existing image fields seem to be ok.

My technical knowledge of Drupal at this advanced level is limited especially as I did not set up this site myself. Rather I just manage it. Also I cannot find any error logs to indicate what is going on in more detail. Where are these located?

Questions Answered.............
CCK version: unknown
imagefield version: It says 7.4 next to the image module and the field module. This is not available in the dropdown above. Can't see any other version options.
permissions for your tmp and files directory. 777
download method (public or private files) Public but it doesn't even get up to this stage
imagefield configuration: not sure??? it is enabled with many different styles in there which are currently used on the site.
expected results: Image field to work and site not to go down.
the unexpected actual results: Image field seems to get added and then can choose more options but the whole site is down.
Steps to reproduce the problem: In admin create a new content type, manage fields, add an image field. Refresh the front end of the site. Error is seen.

This matter is really URGENT. Please help!!!