IT Assistant - CIM connectivity problem - some PCs are in Unknown group

In IT Assistant my servers are OK.

But I try to manage PCs with it... some PCs are OK (green light) and known but some others are in the Unknown group. When I use the diag utility on the unknown PCs and run tests, the first test (CIM connectivity) failed : impossibility to connect to "Windows Name Space". I check the username, password and domain in the config and they are OK.

This test is OK on known PCs with green light in IT assistant.

I reinstalled on failed PCs the "DELL openmanage client instrumentation V7.6", i update BIOS and network card driver... but the CIM test is still "failed".

What I have to do or install on PCs ?????

Many thanks in advance for your help !