hi Juliana,
Thanks for your advice, but I did not find anything about the version of ntp protocol in MS Docs. I don't know why my FW (SN200) found NTPv1 and NTPv2 messages and blocked them because it considered them as unsafe and old.
It's however a fact that NTPv4, or at least NTPv3, is normaly used.
I didn't find any information in w32TM options or register in order to set NTPv4 or v3 mandatory.
If you or anyone knows...