If you are getting the message “The file you are attempting to save or retrieve has been blocked from this Web site by the server administrators.", Windows SharePoint Services 3.0 prevents certain file types from being uploaded to the server. Server administrators can add or remove file types from this list, as needed. Contact your server administrator to request that the file type be unblocked.

To resolve this issue, remove the file type from the Blocked File Types page in Windows SharePoint Services 3.0. To enable a file type that is currently blocked, remove it from the global settings list and from the Web application list. To do this, follow these steps:

1. Start SharePoint 3.0 Central Administration.
2. Click Operations, and then click Blocked file types under Security Configuration.
3. On the Blocked File Types page, click Global Settings in the Web Application box.
4. Remove the file name extension from the list of blocked file types. For example, remove the .config file name extension.
5. Click OK.

If you are using MOSS there are some additional steps.
6. Under Security Configuration, click Blocked file types.
7. On the Blocked File Types page, click the Web application that you want to configure in the Web Application box.
8. Remove the file name extension from the list of blocked file types.
9. Click OK.