Report server report viewer 404 - File or directory not found

With SQL Server 2008 and IIS7, you may run into this error like I did. The fix for me was to do the following:

Under IIS area, double-click on Handler Mappings icon. At the Action pane on your right, click on Add Managed Handler. At the Add Managed Handler dialog, enter the following: Request path: Reserved.ReportViewerWebControl.axd Type: Microsoft.Reporting.WebForms.HttpHandler Name: Reserved-ReportViewerWebControl-axd Click OK.

You may also need to add this to your web.config, although I think this is only for older versions of IIS:

<add name="Reserved-ReportViewerWebControl-axd"
path="Reserved.ReportViewerWebControl.axd" verb="*"
type="Microsoft.Reporting.WebForms.HttpHandler" resourceType="Unspecified"/> in
the <handlers> section.