Hm, lyder underligt - bruger godt nok selv Thunderbird, men det popper selv op når jeg trykker på et link...
Du er med på at du skal fjerne fluebenet ikk'? Vil bare lige være sikker.
Har du prøvet at ændre default e-mail client mens du er logget på som administrator?
Ellers prøv følgende (fra MS support forum):
1. Click the Windows Start button, and then click Run.
2. Type outlook.exe /checkclient. If your computer can't find Outlook, you'll have to type the complete path to your Outlook.exe file, enclosed in quotes (for instance, "C:/Program Files\Microsoft Office\Office\outlook.exe"), followed by a space, and then /checkclient. You can use the Find Files or Folders utility on the Start menu to find outlook.exe.
3. Click OK. Outlook starts and opens a message box indicating which services are not currently managed by Outlook, and asking if you would like Outlook to manage these by default. For example, if Outlook has no default priority, the message is: "Outlook is not currently your default manager for Mail, News, and Contacts. Would you like to register Outlook as the default manager?"
4. Click Yes if you'd like all the options to be managed by default; otherwise, click No.
En hurtig Google søgning viser at der er flere der har problemet, men at det skyldes en fejl under installlationen af Outlook, såfremt man ikke vælger default installation kan det give problemer senere hen. Det er selvfølgelig ikke en tilfredsstillende løsning, men en sidste mulighed er afinstallation efterfulgt af default installation.