Two days ago, ZA Pro informed me that a new update was available. I downloaded it and installed it, but now, whenever the computer starts, I get an error message saying that zlclient.exe was unable to initialize (with error code 0xc0000005) and was being terminated. When I click the "OK" button, the same message pops up one more time. After that, nothing else happens, and ZA Pro is NOT running, leaving my computer unprotected.
The machine in question is running Windows XP Home SP3, with all the latest updates. It is also running the latest version of the free Avira Antivir.
I checked things out with HijackThis, but didn't see anything particularly suspicious.