>>To rule out a problem with the caching you could try temporarily disabling compression - in IIS Manager / Features / Compression.
>
>You mention "temporarily". This means, this default setting should be set as is right?

I think default is to use compression....

>
>>The 1203 code might just be related to someone trying to access an HTTPS page using http://.....
>>
>>Found this: Alert 10. The internal error state is 1203 - From a support forum: "This event is seen on windows 2008 R2 running IIS. If a user tries to access a web site using HTTP but specifies an SSL port in the URL then this event is logged. This event is expected as the client is trying to use the wrong port or the wrong protocol to access the site
>>The error 1203 indicates invalid ClientHello from the client. This is by design and you can ignore this warning."
>
>If it comes from there, I am wondering which this is flagged as red. I am also wondering if this SChannel thing might come from something else. I had the impression that this did not come from IIS. Could it be coming from something else?

I think it's SSL specific. You can set the level of detail provided : http://technet.microsoft.com/en-us/library/dd197492%28WS.10%29.aspx
See also : http://social.technet.microsoft.com/Forums/windowsserver/en-US/4c5430f5-43f6-41b4-97d3-03cfb3efa70b/schannel-error-event-id-36888-is-there-a-way-to-identify-what-causes-schannel-to-log-error?forum=winserverDS

But I think the compression problem is the more likely culprit (between these two)