Webmail service failure: AjaxSoapDoc.CreateFromXml:1

[Labsy]

Hi,
all of the sudden (few days after upgrading to ZCS 7.1.2 + patch) some of users receive this error when they click on INBOX in webmail:

Service failure
---------------------------------------------------
method: AjaxSoapDoc.CreateFromXml:1
msg: Service Failure
code: service.FAILURE
detail: Contact your administrator (invalid SOAP PDU)
---------------------------------------------------

Inbox is displayed without problem initially when user logs into webmail, and he/she can browse all other folders, too. But when user clicks onto INBOX again, this error pops up, and INBOX content is NOT displayed anymore. The only way to see inbox messages is to log-off and log-in again.

Any idea where to start debug?

[Labsy]

Ups...SOLVED! I am fast, hehe.
Firewall content filter issue after uploading new rules.