Hello,
during last few months I got these strange synthoms:
sometime (randomly) I see in the same page 2 different modules of 2 different portals.

DETAILED SYNTHOMS
1.a) in a page (randomly any page) sometime I see 2 modules; the first module is the one I put in the page; at the bottom of the page I can see another module (or just part of it) that is a module of another portal of the same DNN instance.

1.b) other times (randomly) I see my page but skin or part of it is from another portal; so it seems that output for a  client request is messed up mixing output from 2 different portals.

2) I can not reproduce it because I can refresh the page but it does not happen again.

3) in Log I can see errors like this one:
"...DotNetNuke.Services.Exceptions.PageLoadException: The state information is invalid for this page and might be corrupted..." 
"...System.FormatException: Invalid character in a Base-64 string. at System.Convert.FromBase64String(String s) at System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) at System.Web.UI.ObjectStateFormatter.System.Web.UI.IStateFormatter.Deserialize(String serializedState) at System.Web.UI.Util.DeserializeWithAssert(IStateFormatter formatter, String serializedState) at System.Web.UI.HiddenFieldPageStatePersister.Load() --- End of inner exception stack trace --- --- End of inner exception stack trace --- at System.Web.UI.ViewStateException.ThrowError(Exception inner, String persistedState, String errorPageMessage, Boolean macValidationError) at System.Web.UI.HiddenFieldPageStatePersister.Load() at System.Web.UI.Page.LoadPageStateFromPersistenceMedium() at System.Web.UI.Page.LoadAllState() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---"

ENVIRONMENT:
1) dnn ver 4.5.3
2) win 2003 server (SQL Server 2000 is on another machine)
2) We have developed and installed in these portals some PA modules (few of them use asp.net AJAX)
4) setting Host --> Performance Settings (default setting):
Page State Persistence: page
Module Caching Method: disk
Performance Setting: moderate caching
Authenticated Cacheability: ServerAndNoCache
Compression Setting: no Compression
Use Whitespace Filter: unchecked

Any ideas?

Thaks in advance

Luca
Italy

leupold,
thanks for your help

1) we do not use pageblaster or any http compression module (do not use http compression at all)
2) I could see this problem from our lan (we have proxy server) but also from my pc at home (no proxy server) and also some customers reported this error (no proxy server).

Bye
Luca