The problem may be the memory allocation in your php.ini file. I'm not an expert at this, but found a hint on the web about how to change it and it solved the problem you've been experiencing (that I did too). I simply inserted this line in my php.ini file:
memory_limit = 16M ; Maximum amount of memory a script may consume (8MB)
I think the default is 8MB
The article on how to change memory is here:
www.wallpaperama.com/forums/how-to-change-memory-limit-php-apache-server-t53.html
Good luck,
Ted