Show excerpt

I have several post already on my blog that were posted while the setting in theme options was set to show full content.  I changed the option to 'show excerpt' and when I select 'continue reading'  I get a '500 internal server error' for these and any new post. I would also like the full image to show on the home page.  I have set all three media sizes to be 1024X1024 but it does not affect the featured image size. In addition,  is it possible to have the excerpt text to show to the right of the featured image? Thanks Kat www.blog.bluezelia.com  (I will remove the 'show excerpt option until I can solve as I don't want my site to be down)