Kereberos delegation problem

[יבש]

Although I enabled Kerberos delegation, and checked that it worked for a
given asp.net application (a closed solution - no source code), I can not
make it work in my own solution. The working scenario is Client (browser) ->
IIS -> Sql, while the none-working one is Client (browser) -> IIS -> IIS. If
I check for Kerberos network traffic on the middle tier (using a network
monitor), I can see that my solution does NOT trigger any Kerberos messages
at all while the given one does. Any ideas? Is there some special code that
my solution must implement in order to use Kerberos delegation correctly?
Currently I am just passing on CredentialCache.DefaultCredentials.