When using WebShell, users have the option to search with a Find Field, to narrow down fields in a particular node. However, when users who are non admins attempt to use this field, they receive "error: An unknown error occurred during the request. This could indicate a request to an invalid endpoint or a problem with the web server configuration."
Download and install the latest patch, which contains all fixes from previous patches. If you are running an older version, download and install the latest version and then the patch.