Problem accessing web service via https with integrated security

[jacorona]

Hello all,
I have found a problem accesing a web service hosted in IIS 5.0 in a W2K box.
The web service site is configured to accept both integrated windows authentication and client certificates.
I have a WinForm 2.0 client application and when it presents a certificate it works fine, but when it tries to access the web service using integrated security it times out.
Both accesses are via an https: uri.
Moreover, an .aspx page in the same site is browsable from IE without any problems (either presenting a certificate or with integrated security). Even the webservice is accessed without problems from the browser (requesting the .wsdl, for instance).
Any clue why accessing the web service form a client application via https: and integrated security times out and when using certificates it doesn't?
Many thanks for your help.