Replace your code of
web.config
file
<configuration><br />
<system.web><br />
<customErrors mode="RemoteOnly" defaultRedirect="mycustompage.htm"/><br />
</system.web><br />
</configuration>
by the following lines
<configuration><br />
<system.web><br />
<customerrors mode="Off" /><br />
</system.web><br />
</configuration>