Is this your own server or a share host? Do you expect some have load? Is a securiy pack installed like mod-security? This can cause trouble if the parameters set to small.
Blank pages also comes up if the server kill the script execution due execution time restriction or memory problems.
Another source of blank pages can be corrupted languages files.
Your log looks stange. File does not exits messages while try to watch a posting sound like server problems. The webserver is unable to access the filesystem where the files be.
Do you exceed your file quota?
