Take a look at PHP memory_limit req, a page that has been hit over 17 thousand times! TikiWiki wants 32megs as the memory_limit. Anything less is asking for trouble.
After you install you can learn all about these limits by running the program PHP Info, which is the bottom most menu item after logging in as Admin. (http://www.YourSite.com/tiki/tiki-phpinfo.php). Run that and search for three values on your ISP’s server:
max_execution_time = 300 ; Maximum execution time of each script, in seconds
max_input_time = 60 ; Maximum amount of time each script may spend parsing request data
memory_limit = 32M ; Maximum amount of memory a script may consume
From my personal experience an 8M memory limit can bomb sending out just 50 newsletters. I'm told the upper bound for this would be around 4000 on a very well kept server with the full 32M memory_limit.
Do not assume because your ISP has Fantastico or some other install script or advertises TikiWiki as supported that they have any experience whatsoever in this. Few offer more than the 8MB install default of PHP so be advised. The problem doesn’t surface till the loading starts. --RickL
Choose your tiki version for the FTP install guide by clicking the version numbers above.