The message 'Explorer has caused an error in <unknown>'..... is almost
certainly related to your PC being infected with viruses or other malware,
especially commercial parasites.  You need to clean up your PC using not
only your preferred anti-virus application but also various other tools
listed below.  As to how to remove specific viruses check the details for
the viruses concerned on your AV applications web site.  Note that the
items you listed are not viruses as such but instead trojans and parasites
and thus often not targeted by anti-virus applications.  For more details
of the StartPage-DU Trojan see http://vil.nai.com/vil/content/v_126244.htm

If you haven't already done so I would strongly recommend that you check
your system for possible viruses using your preferred anti virus
application equipped with an updated set of viral signatures.  However you
might first want to check your PC using one of the online virus checks
such as McAfee's online checker
(http://us.mcafee.com/root/mfs/default.asp)  or Trend Micro's Housecall
(http://housecall.antivirus.com).

This might be a good time to download yourself a copy of the free Ad-Aware
SE Personal edition from Lavasoft
(http://www.lavasoftusa.com/software/adaware/) and also SpyBot Search &
Destroy 1.3 (http://www.safer-networking.org/) and use them to check your
system for other commercial parasites remembering that they are only as
good as when you last updated their reference files.  I also use a program
called BHODemon (http://www.definitivesolutions.com/bhodemon.htm that
checks for unwanted Browser Help Objects and SpywareBlaster
(http://www.wilderssecurity.net/spywareblaster.html) which can help
prevent some parasites getting a grip on your PC.

Just is case the problem is due to a new version of the CoolWebSearch
parasite you might want to download and run the CWShredder which targets
that specific parasite. Unfortunately neither AdAware or SpyBot seem to be
able as yet to fully detect all the various versions of the CoolWebSearch
parasite as it keeps changing.  The latest version of CWShredder can be
downloaded (free) from
http://www.intermute.com/spysubtract/cwshredder_download.html

Finally if you still continue to experience problems download a copy of
HijackThis from (http://www.spywareinfo.com/~merijn/downloads.html).
Create a folder called HJT on C: (not on your desktop nor in your temp
folder) and copy the file you downloaded to that folder. Close as many
applications as you can including all instances of Internet Explorer.
Enable Explorer to see all files and folders (Tools | Folder Options |
View and check "Show hidden files and folders" and uncheck "Hide protected
operating system files") and then run hijackthis.exe and post back the log
to either the HijackThis Forum at http://forums.spywareinfo.com/ or
alternatively http://forum.aumha.org/viewforum.php?f=30 and hopefully this
will enable someone to identify the cause of your problem.

See also: Dealing with Unwanted Malware, Parasites, Toolbars and Search
Engines http://mvps.org/winhelp2002/unwanted.htm and also Browser
Hijacking http://www.spywareinfo.com/articles/hijacked/