Zimbra Forums

I am assuming you are talking about Modern UI
This issue is reported in ZBUG-5358

Check logs it might have more details about failure

This zimlet is only available in Network edition, are you using FOSS or network edition?

Looking through posted log, below line seems unusual As far as I know, in Zimbra installation jetty uses the zimbra user and not the default jetty user. So this might be some configuration corruption issue.

This zimlet is used to switch clients (Classic to Modern and vice versa) so for FOSS edition users this zimlet will not add much value as Modern UI is not available in FOSS edition.

Which OS? And are you using the network edition build/license?

Yes you will need network edition license to get access to Modern UI

This issue is getting tracked in https://synacor.atlassian.net/browse/ZBUG-4620

Yes we have hardened some policy rules, so multiple requests coming in very short time might be considered as abuse of the system and it will show this issue for short period of time.

We have tried to fix this issue. Let us know if anyone still encounters these errors.