You receive an error message when you try to open a file type that was blocked by your registry policy settings in PowerPoint 2007/2003

This issue may occur if an administrator has restricted the types of presentations that you can open in Microsoft Office PowerPoint 2007 or in Microsoft Office PowerPoint 2003. An administrator can set a registry key to restrict this functionality.
To resolve this issue, disable the restriction on opening presentations that were blocked by the registry settings of PowerPoint. To do this, use a trusted location, or create an exempt location:

• In PowerPoint 2007, if you trust the file that you want to open, you can move the file to a trusted location to override the registry policy settings.For more information about how to create, to remove, or to change a trusted location for files, visit the following Microsoft Web site:
  http://office.microsoft.com/en-us/help/HA100319991033.aspx
• In PowerPoint 2003, there are no trusted locations. You can create an exempt location to override the registry policy settings. To create an exempt location, follow these steps:
• 
  1. Exit PowerPoint 2003.
  2. Click Start, click Run, type regedit in the Open box, and then click OK.
  3. Locate and then click one of the following registry subkeys:
  HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Common HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\11.0\Common
  4. On the Edit menu, point to New, and then click Key.
  5. Type OICEExemptions for the name for the key.
  6. On the Edit menu, point to New, and then click String Value.
  7. Type a string name, and then press ENTER. For example, type ExemptDirectory.
  8. Right-click the string name that you typed in step 7, and then click Modify.
  9. In the Value data box, type the path of the directory that contains the file, and then click OK. 10. On the File menu, click Exit to exit Registry Editor.

Go to PowerPoint 2003 Solution Center at http://support.microsoft.com/ for more troubleshooting tips.