I actually found the same problem since upgrading to 2.8, but I do have access to my logs on FreeBSD. I'm using a /data directory that was copied over from 2.7 and was working fine then. Since the upgrade process is manual, I think that's where the problem stems from. I backed up my entire selfoss directory, created a new one (inheriting permissions from the parent directory), adjusted the config and then copied back my data directory. It doesn't like the permissions changes, see:

[Wed Jul 31 16:15:33 2013] [error] [client 2.2.2.2] file_put_contents(data/favicons/cc606f5f42c7dba13eb5cc2d42081b08.png): failed to open stream: Permission denied

Previously the permissions were as follows:

drwxr-xr-x 7 me www 512 Jun 20 2012 data

Clearly that's incorrect, as according to the log we need full access for myself (7), read/write access for the www user (6), and read-only access for everyone else (4). So I simply went into the /data directory and did a "chmod -R 764 favicons" and all is well now.

drwxrw-r-- 2 me www 2048 Jul 26 00:01 favicons

Kelly