W3 Total Cache crashes, if too many users online!

Hallo =)

I installed W3 Total Cache and was very amazed about the good performance.

The only Problem is:
If I get on my best visited days many people at the same time online, W3 Total Cache stops working an shows me following Errors:

It appears Page Cache URL rewriting is not working. If using apache, verify that the server configuration allows .htaccess or if using nginx verify all configuration files are included in the configuration.

It appears Minify URL rewriting is not working. If using apache, verify that the server configuration allows .htaccess or if using nginx verify all configuration files are included in the configuration.

After a while, when the traffic calms down, the Problem disappears and the site is very fast in loading again and W3 Total Cache is working perfectly.

To say it short:
On days with under 10.000-15.000 visitors a day, W3 Total Cache is running perfectly.

On days with over 10.000-15.000 visitors a day, W3 Total Cache stops working and shows me these two errors above.

I would be very happy if someone could share some advices!
=)