Server Error in '/' Application.

wha is this?
----
Server Error in '/' Application.
Runtime Error
Description: An application error occurred on the server. The current custom
error settings for this application prevent the details of the application
error from being viewed remotely (for security reasons). It could, however,
be viewed by browsers running on the local server machine.

Details: To enable the details of this specific error message to be viewable
on remote machines, please create a <customErrors> tag within a "web.config"
configuration file located in the root directory of the current web
application. This <customErrors> tag should then have its "mode" attribute
set to "Off".

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

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


Notes: The current error page you are seeing can be replaced by a custom
error page by modifying the "defaultRedirect" attribute of the application's
<customErrors> configuration tag to point to a custom error page URL.

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

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

 

By default, ASP.NET error message hides details about errors. Go to
the Web.config file and find customErrors section inside <System.web>.
By default, this section has

<customErrors mode="RemoteOnly" />

Change it to

<customErrors mode="Off" />

This should help you to see the detailed error message when error
occurs again.

You can also go to Event Log to see what was wrong.