Why do you set such high memory limits in the quick cache plugin?
these trigger suhosin warnings and it's generally a bad idea to try and force settings higher than the default php settings.
(I have to modify your code every time I update to ensure they're not crazy high)
Could you perhaps try and code this plugin a little better next time, and adhere to the php defaults?
Setting a memory limit of 512M of ram is a little much when some low end webservers will only HAVE this amount of ram available.