Next time please do a search before posting, this is a common problem and has been answered many times.
Download COMDLG32.OCX: http://www.ascentive.com/support/new/images/lib/COMDLG32.OCX
Back up your current copy of COMDLG32.OCX and copy the new version to the same file location. This file should be located in the WINDOWS\SYSTEM directory on your C: drive (for Windows NT and 2000: \WINNT\system32).
Using your mouse, click on the "Start" button and then click on "Run".
According to your Operating System, type the following command to register this library file:
Windows 95, 98, or Me:
Windows NT or 2000:
You should see a message saying "DllRegisterServer ... succeeded"