Add This code to your web.config
<configuration>
<system.web>
<customErrors mode="Off"/>
</system.web>
</configuration>
Since when you do not add this tag, IIS hides the errors from users that are not locally on the webserver.
After you do that reopen the website, the error should appear clearly. if you still want help. paste the error it causes so We can help.
best Regards,
Ibrahim Karakira