Further checking reveals the ZA is using the TDI filtering.
The ZA for Vista is built on the strictly on the Microsoft Windows Filtering Platform API and the TDI has been discontinued for the Vista releases of the ZA.

More often than not, if there is a conflicting .dll injected the LSP or a rogue malware .dll present, this can still cause issues. Although not directly with the TDI filtering of the ZA itself.

Best regards.