SoapHeaderException: Message Expired

[Kim]

Hi,
I am working on a web server that clients can upload/download files using
WSE2.0 sp3. Files are DIME-attached to a soap message. The web server accepts
files without any problem when the files are smaller than approx. 30MB. But
it generates SoapHeaderException: Message Expired error when a file is bigger
than 30MB. It usually takes 10 to 15 minutes to get the error.
I tried to put right configuration here and there but made no success. Can
anyone take a look at the following and tell me anything I missed?
The server is to allow files less then 100MB, and it times out after 100
minutes.

//machine.config
<httpRuntime executionTimeout="6000" maxRequestLength="102400"...

//web.config
<sessionState...
...timeout = "100"...

<microsoft.web.services2>
<messaging>
<maxRequestLength>-1</maxRequestLength>...

//server code
....
SoapContext.Security.Timestamp.TtlInSeconds = 0; //for response
....

//client code
....
WebServiceWse proxy = new WebServiceWse();
proxy.Timeout = 6000000; // 100min
....
SoapContext.Security.Timestamp.TtlInSeconds = 0; //for request
....
Thank you in advance!
-- Kim