This is possible my fix didn't work, because I do a substr starting at 16, but I don't know what is in your "/w3tc-config/master-admin.php" file.
On the svn I can see a change in the method W3_ConfigData::get_array_from_file()
You can fix it by replacing line 134/135:
$content = @file_get_contents($filename);
$config = @eval(substr($content, 5));With :
$config = include $filename;
This will do the trick, I just tested it and it work.
I don't know if the dev of this plugin will read this but :
I do not recommand to use "serialize/unserialize" for configuration, I recomand json_decode/encode.
Serilize implementation can change between PHP versions, so it could break compatibility whereas json never change.
More, json_decode/json_decode are faster than serialize. (but they do not manage Object, and here the configuration is an Array)