Hello Neo.
1 - Yes, exactly. OU's created before DirSync deployed won't sync to my Office365 tenant. When i create a new one, it syncs, even if a move a user created before deployment of DirSync. Also, if i create a new user inside old OU, it also sync.
2 - The error message don't appear anymore. What i did was move the users from the OU again and deleted the OU. Force a sync with Powershell script. After the sync was completed without error, i created the OU again with the same name as the old OU and forced a sync again. When completed, again with no error, i moved the users back to the OU and did a sync for the third time. I got no error until now. But the users inside OU, this one or another "old" OU are still not appearing on Office365.
3 - No, there is no error when the "old" user in the "old" OU is not synced to Office365. But now, like i said on previous point, there's also no error when they are synced, the problem is that they don't appear on Office365.
4 - Yes, i have SBS 2003 with Exchange.
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Meanwhile i'm trying a few more steps to troubleshoot this issue. I'm trying to follow technet.microsoft.com/.../jj710171.aspx to get this issue solved.