Web.Config Error

I have developed Web Application in c#.Net i have uploded it on the server But when access it gives an error as following

<!-- Web.Config Configuration File -->

<configuration>
<system.web>
<customErrors mode="Off"/>
</system.web>
</configuration>

<!-- Web.Config Configuration File -->

<configuration>
<system.web>
<customErrors mode="RemoteOnly" defaultRedirect="mycustompage.htm"/>
</system.web>
</configuration>