Click Start>Find>Files or Folders.
In the "Named" box, type:
*.cpl
and in the Look In drop-down box, select the C: drive.
Click Find Now.

Maximise the window and click on the heading "In Folder" to sort the files by directory.  Look at the files listed in the \Windows\System directory.

Double-click each file in turn...if some work, but one of the files gives you the error, that Control Panel file is corrupt.

The System control panel applet is the Sysdm.cpl file....the Network applet is Netcpl.cpl

To fix the error you must replace the .cpl file using the 'Extract one file' option of System File Checker (SFC), and extract it to the Windows\System folder.

How to use System File Checker (SFC) to extract a file:
http://support.earthlink.net/mu/1/psc/img/walkthroughs/windows_9x_nt/dialers/dun
_1.3/0850.how.to.sfc.psc.html
and
http://users.westelcom.com/rogersr/sfc.htm#1pp

HOW TO: Extract Original Compressed Windows Files:
http://support.microsoft.com/default.aspx?scid=kb;EN-US;129605#5

Description of Control Panel (.cpl) Files
http://support.microsoft.com?kbid9648

How to Troubleshoot Control Panel Issues in Windows
http://support.microsoft.com?kbid)9923