Hi,
I had the same problem. According to the code, system is unable to create a cache file.
The variable $file is not correctly set, so it tries to create a file in the “root” directory of the host filesytem.
I modified the code in this way:
$file = “/<the_full_path_to_the_dir>/wp-content/plugins/flickr-photostream” . “/” . $reqhash . “.cache”;
And the problem was solved. It’s just a dirty workaround!
Regards!