I recently moved my installation to another server.
I tried editing a template, but only the admin header was displayed and I received the following error messages:

[phpBB Debug] PHP Notice: in file /includes/acp/acp_styles.php on line 784: array_diff() [function.array-diff]: Argument #1 is not an array
[phpBB Debug] PHP Notice: in file /includes/acp/acp_styles.php on line 844: Invalid argument supplied for foreach()

I set recursively set all files in /styles/ to 755 and the error disappeared.

The function filelist() in functions_admin.php does not return any error if the directory isn't readable. I'd recommend that.