In der Registry unter Hkey Classes Root stehen die Dateinamenerweiterungen beginnend mit einem Punkt, z.B.
.AVI
der letzte Eintrag ist meist .ZIP
Die Liste durchschauen-wenn sich extrem lange Einträge finden (mehr als etwa 20 Zeichen, meist deutlich zu sehen, weil weit darüber), diese Löschen, dann stürzt die DLL nämlich ab.
Rechner neu Starten, voila, Problem gelöst

Maybe everyone should send the cost of repairs to Bill Gates maybe next time he wont screw up....

To use the Internet Explorer Repair tool:

Click Start , point to Settings , click Control Panel , and then
double-click Add/Remove Programs .
On the Install/Uninstall tab, click Microsoft Internet Explorer 5 , click
Add/Remove , click Repair the current installation of Internet Explorer ,
and then click OK .

If the Internet Explorer Repair tool detects an error, you may receive an
error message that is similar to the following error message:
Internet Explorer 5 cannot be repaired. Please reinstall Internet Explorer
5.
If you click Details , you may receive an explanation for the problem. For
example, you may receive any of the following explanations:
Internet Explorer 5 cannot be repaired due to the following errors:
File file_name is missing.
-or-
Internet Explorer 5 cannot be repaired due to the following errors:
Version 4.72.3110.0 of file file_name exists but needs to be greater than
5.0.808.1000.
To resolve either of the problems that are associated with these error
messages, it is recommended that you reinstall Internet Explorer 5.x

NOTE : The result of the repair process is logged in the "Fix IE Log.txt"
file that is located in the Windows folder.
The Internet Explorer Repair tool repair process may vary slightly,
depending on the operating system that you are using.

If all else fails, remove Internet Explorer from your computer, find the shdoc401.dll file (I think it is in the Shell32 directory), and delete it before reinstalling or upgrading your version.

Hope this helps...