Hello there,
Just fought and fixed the same issue. It was our first time using SSL in Altiris and my NS was choking on the overhead caused by https traffic.
1. On the Notification Server, navigate to %windir%\System32\inetsrv and copy the applicationHost.config file to a safe location
2. While still on the Notification Server, open an elevated command prompt and execute the following command without line breaks.
appcmd.exe set config "Default Web Site/Altiris" -section:system.webServer/serverRuntime /uploadReadAheadSize:"1048576" /commit:apphost
You should recieve output to the effect of "Wow that was successful" (or something similar)
3. Restart IIS and give it another try. Magically, the SSL traffic has enough room to breath and the error shouldn't bother you anymore.
CAUTION NOTE: If something should go wrong, simply stop IIS, replace your applicationHost.config file with the one that you carefully copied to a secure location and restart IIS.