http://www.iisworks.com/faq/kb.asp?a=show&ID=249

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KB249: I have problems uploading with ASP Upload or file edit 
Category: ASP FileMan, ASP KnowledgeBase, ASP... | Updated: 8/12/2005 8:12:07 PM | Owner: JH | Read: 7427 (Last: 2/27/2009 3:11:02 PM)

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Description
I have problems uploading with ASP Upload or editing:
- EventID 5: Unexpected error/Operation not Allowed 
- ASP Error "ASP 0104: 80004005"

Resolution
The following might help for IIS6 (Server 2003):

IIS6.0 prevent the upload of files more than +200Kb. So you need to make some changes in the default IIS settings. Change the ASPMaxRequestEntityAllowed to 1073741824 in the C:\WINNT\system32\inetsrv\metabase.xml file. In IIS6, this value determines the maximum size POST to the website and if it isn't set high enough will prevent you from uploading files.

Also make sure to check the general troubleshooting FAQ. Proxies and virus scanners are known to cause strange behavior of web applications in some cases.