If you install more than a few modules in your Drupal implementation the chances are that it’ll run out of memory and you’ll start seeing blank pages and odd behaviour. The fix for this is to increase the amount of memory allocated to PHP, which you can usually do in your php.ini file. But if your hosting is Rackspace Cloud Sites you don’t have access to the php.ini file. You must instead put your PHP settings in a .htaccess file in the root directory of your hosting space.
Here’s some example settings:
php_value memory_limit 96M php_value upload_max_filesize 50M php_value post_max_size 50M
Now, here’s the important bit: once you’ve made put those lines in your .htaccess file and FTP’d it to your webspace, the changes might not appear to have taken effect. I had to delete the original .htaccess file and upload a fresh one for my changes to be picked up. Hopefully this might help somebody else in the same situation.
N.B. Rackspace’s support had next to no idea of what I was talking about. Their Livechat support service was as useful as telephoning someone in a library and waiting while they went off to find the information. They obviously don;t support individual applications hosted by them, but I’d have expected a little more help.