So you installed Owncloud and get a HTTP-500 error for some preview-image: /index.php/core/preview.png?x=36&y=36&file=%2F%2FownCloudUserManual.pdf&c=53b5540ae7d0e

Error in the admin-interface: Postscript delegate failed `/tmp/a1blah2c1774205d9ae418a572cdc38pdf': No such file or directory @ error/pdf.c/ReadPDFImage/677

Install ghostscript. W(