Edwin, do you have the recommended memory requirement for running a Sitefinity website?
Sitefinity recommends 500+ MB of memory to run a Sitefinity website, but if you have more, use it. You can read more about that at this URL...
Also, something I have done in the past is generate my own machineKey in the web.config file. I have seen this used when Sitefinity is deployed in a shared web hosting solution. Below is a great article from code project that will show you how to add this to your web.config.
Let me know if either of these items will help.