This is due either to corrupt QC client components or conflicting applications on the client machine.  It is most likely because of an Internet Explorer toolbar or add-in.
Give this a try:
1)  First, try uninstalling the QC client components using the QC Client Uninstall Utility:
[http://support.openview.hp.com/selfsolve/document/KM1400068
][1]
2)  If the problem still persists, remove the ''MSN Toolbar'' or ''Web Discussion'' toolbar from the client machine (IE -> View -> UNCHECK 'Discuss' under Explorer Bars).
3)  Take a look at the list of Windows applications that are known to conflict with the QC Client and remove/disable as appropriate:
[http://support.openview.hp.com/selfsolve/document/KM176429][2]
4)  If the user wants an alternative to removing conflicting applications, try using QC Explorer instead of IE (found in the Add-ins Page).
Reference:
[http://support.openview.hp.com/selfsolve/document/KM195818][3]
  [1]: http://support.openview.hp.com/selfsolve/document/KM1400068
  [2]: http://support.openview.hp.com/selfsolve/document/KM176429
  [3]: http://support.openview.hp.com/selfsolve/document/KM195818