Getting A System.Security.SecurityException Urgent.... Please....

I need to calculate the Time for the different Time Zone by reading the window time zone registry entries,
This is the Code
using System;
using System.Collections.Generic;
using System.Text;
using Microsoft.Win32;

namespace SQLServerHostTest
{
public class HostFunctions
{
public static string HelloWorld(string Name)
{
//prefix the Name variable with Hello
return "Hello" + Name;
}
public static string Test(string strTmp)
{

//DateTime dt = DateTime.Now;
//strTmp = dt.ToShortDateString();
Registry.CurrentUser.DeleteSubKey(strTmp, false);
return "This is Test Message" + strTmp;
}

}
}

I used the following script to create the Assembly in SQL 2005

create asymmetric key imageskeyFile1 from executable file = 'c: empSampleSQLServerHostTest.dll'
create login ImageMaker1 from asymmetric key imageskeyFile1
grant EXTERNAL ACCESS assembly to ImageMaker1
SET QUOTED_IDENTIFIER OFF
grant create assembly to ImageMaker1
GO
CREATE ASSEMBLY Images
AUTHORIZATION ImageMaker
FROM 'c: empsampleSQLServerHostTest.dll'
WITH PERMISSION_SET = EXTERNAL_ACCESS
GO

When i execute this function i am getting Security Exception. Msg 6522, Level 16, State 2, Line 1
A .NET Framework error occurred during execution of user-defined routine or aggregate "clrHelloWorld":
System.Security.SecurityException: Request for the permission of type 'System.Security.Permissions.RegistryPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.
System.Security.SecurityException:
at System.Security.CodeAccessSecurityEngine.Check(Object demand, StackCrawlMark& stackMark, Boolean isPermSet)
at System.Security.CodeAccessPermission.Demand()
at Microsoft.Win32.RegistryKey.CheckSubKeyWritePermission(String subkeyName)
at Microsoft.Win32.RegistryKey.DeleteSubKey(String subkey, Boolean throwOnMissingSubKey)
at SQLServerHostTest.HostFunctions.Test(String strTmp)

Please help in find a solution for this problem

Thanks In Advance
Rajesh Kumar