We have discovered problems running EPiServer4 under Windows 2003 Server with SP1 installed. 

Symptoms:

Files larger than approximately 60k can not be opened through EPiServer's UnifiedFileSystem. 

The source of the error seems to be within the OS/.NET environment. We have reported this problem to Microsoft and they have confirmed that they can reproduce the error in a non-EPiServer ASP.NET environment. Investigation is currently underway. 

We still recommend the use of SP1, but if you intend to use Unified File System you need to get the hotfix from Microsoft. 

Update 060421

Microsoft seems to have created a kb regarding this issue. You can find it at the following adress, http://support.microsoft.com/?kbid=902780.

Update 050617

We previously received an experimental hotfix from Microsoft which we determined to solve the issue. We have not been given permission to redistribute this hotfix but we will be contacted when a public hotfix is available, so far we have not received any further information.

These are the KB article number given to us:

KB Article Number(s):  894611, 888420

Should you wish to obtain a fix for this issue we recommend that you contact Microsoft Support and ask for the hotfix related to these articles.