You are trying to upload multiple documents to a SharePoint 2010 document library.
You can successfully use the multiple upload page and upload documents from a client machine which has Office 2010 installed using the drag and drop interface.
However, when you use a client which has Office 2007 installed and you use the multiple upload page, you are presented with an explorer-like interface to select multiple files. You select some files and click ok.
The screen refreshes and the documents are not uploaded.
Furthermore in the IIS log of the SharePoint website you can see the following request with a 404 'File not Found' response:
POST /_vti_bin/shtml.dll/Documents/Forms/Upload.aspx Mozilla/4.0+(compatible;+MSIE+5.0;+Windows+NT+5.0)+[Sharepoint+Active-X+Upload+Control] 404 0 0 106
This is caused by an incorrect handler order in IIS configuration at the server level or at the website level. In order to allow Office 2007 client multiple upload requests, the "PageHandlerFactory-Integrated" handler must be listed below the "ISAPI-dll" handler on the IIS administration / Handler Mappings / View Sorted List page.
Before changing any IIS settings it is recommended to take a backup of current configuration. Run the following command from an administrative command prompt that is set to c:\window\system32\inetsrv> appcmd.exe add backup beforeHandlerMappingChange
Open IIS manager Click on the server name at the top left of IIS manager. Click on Handler Mappings and then click “View Ordered List” on the right-hand pane. Locate the "ISAPI-dll" and click Move Up until it is listed above "PageHandlerFactory-Integrated."
If the handler order has been modified on the website level you will need to repeat the previous steps on the IIS website which belongs to the affected SharePoint web application.