Also, please understand that the same friendly error page is shown no matter what the error is. This is a security feature so we don't give hackers feedback about any errors they may cause. Errors can be reviewed from Administration Menu > System Log or by viewing the file /Data/currentlog.config file in a text editor.
You can also turn off the security feature to see the details by changing RemoteOnly to Off in Web.config
<customErrors mode="RemoteOnly" defaultRedirect="Error.htm">
<error statusCode="404" redirect="~/PageNotFound.aspx" />
</customErrors>
So no conclusion about errors can be made until seeing the error detail.
Best,
Joe