After opening a call to MS, they give us the patch for KB 957511. We are not concerned by this KB but it contains a more recent version of DLL Momnetworkmodules.dll, which does TCP and web applications tests. Once this dll updatedn the problem was gone.
By the way it could have been necessary to register again this dll with:
regsvr32 “c:\program files\system center operations manager 2007\momnetworkmodules.dll”