UDT Using Format.UserDefined And Hashtable -&&> Security Error In SQL 2005

I am developing a UDT using Hashtable as the member of the UDT and the UDT is defined as Format.UserDefined. After deployed in sql, I tried the UDT as below:

declare @_prodtype ProductSearch

SET @_prodtype = Convert(ProductSearch, 'Product,Certification;Region,China')

where ProductSearch is the UDT.

The error occurred:

Msg 6522, Level 16, State 2, Line 3

A .NET Framework error occurred during execution of user defined routine or aggregate 'ProductSearch':

System.Security.SecurityException: Request failed.

System.Security.SecurityException:

at System.Security.CodeAccessSecurityEngine.ThrowSecurityException(Assembly asm, PermissionSet granted, PermissionSet refused, RuntimeMethodHandle rmh, SecurityAction action, Object demand, IPermission permThatFailed)

at System.Security.CodeAccessSecurityEngine.ThrowSecurityException(Object assemblyOrString, PermissionSet granted, PermissionSet refused, RuntimeMethodHandle rmh, SecurityAction action, Object demand, IPermission permThatFailed)

at System.Security.CodeAccessSecurityEngine.CheckSetHelper(PermissionSet grants, PermissionSet refused, PermissionSet demands, RuntimeMethodHandle rmh, Object assemblyOrString, SecurityAction action, Boolean throwException)

at System.Security.CodeAccessSecurityEngine.CheckSetHelper(CompressedStack cs, PermissionSet grants, PermissionSet refused, PermissionSet demands, RuntimeMethodHandle rmh, Assembly asm, SecurityAction action)

at ProductSearch.Parse(SqlString s)