Based on the provided information it seems that the error you are getting is most likely coming from your server configuration. I would like to note that the following article can be very useful when deploying a Sitefinity website on IIS:
1. Verify that the Application Pool Identity is NetworkService.
2. Check the Authentication section of your website in IIS. Verify that only Anonymous authentication is enabled and the anonymous user identity is the application pool identity.
3. Assign proper permissions over the App_Data folder for the NetworkService account
Aside from the issue I want to note that your current version of Sitefinity - 4.2.1650.0 is very old and I would suggest you to consider upgrading the project as we have included numerous bug fixes, new features and optimizations in each major version of Sitefinity after 4.2.1650.0 which will improve significantly your Sitefinity experience.More information about the upgrading process could be found in our Sitefinity documentation
There is a similar case discussed in the following thread:
In all cases the reported problem was related to the hosting environment ( all users encountering similar symptoms when browsing their projects ) which was always a shared hosting environment with limited resources, which were in conflict with Sitefinity. For example if there is not enough memory for the CMS or there is some restriction ( permission ) which was preventing the system to pass the requests.
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