Problem importing to WSUS error 80131509

I have a wsusmachine (3.1.6001.65 on win 2003 R2 with update Wintrust
KB938759). Updates are working as they should.
But when I try to import Vista Service pack 1 from Microsoft Update Catalog
I get an error. And when try to import something else as well.

The error:

Some updates could not be imported.
[Error number: 80131509]
The following are common causes and solutions for this issue:
If you use a proxy, be sure that it is the same proxy being used by your
Windows Server Update Services (WSUS) server. Your WSUS server might not be
configured correctly. Contact your WSUS administrator.

Any ideas?

Found one suggestion that you could not import to a downstream server but
this is the only wsus-server.


from the logfile: "mucataloglog.txt"
2008-04-09 13:58:45:014 4796 c08 MUP Enter
CMUCatalogWebControl::ImportToWsus.
2008-04-09 13:58:45:014 4796 c08 MUP FATAL: Invoke() failed for method
GetRemoteUpdateServerInstance.
2008-04-09 13:58:45:014 4796 c08 MUP FATAL: Exception message:"The
underlying connection was closed: An unexpected error occurred on a send.".
Exception Source:"Microsoft.UpdateServices.Administration". scode=0x80131509.
2008-04-09 13:58:45:014 4796 c08 MUP FATAL:
MUP:CMUCatalogWebControl::ImportToWsusCore: GetIUpdateServer() failed with
0x80131509.
2008-04-09 13:58:45:014 4796 c08 MUP FATAL:
MUP:CMUCatalogWebControl::ImportToWsus: ImportToWsusCore() failed with
0x80131509.
2008-04-09 13:58:45:014 4796 c08 MUP Leave CMUCatalogWebControl::ImportToWsus.