Zextras Client Zimlet installation failed

Hi,
i've upgraded today to version 2.2.4 without any warning or error.
After the installation i went to the admin console, i got a warning that Zextras Client Zimlet needed to be installed to be able to use some features, but the installation fails with this message:

Unable to deploy ZxChat Zimlet: Permission denied

I also tried run this command as Zimbra user:
zimbra@zcs-mail-01:~$ zxsuite core doDeployClientZimlet

I'm using Ubuntu 14.04 and Zimbra 8.6.0.

What i'm missing? thanks