Verifique primeiro este artigo da O Vista não pôde executar esta operação porque o cliente de e-mail padrão não está instalado corretamente :
Customer recently bought a Vista PC.
After a few weeks he started getting a strange error message:
Could not perform this operation because the default mail client is not properly installed.
This would happen whenever he would click on a mail link within internet explorer.
It didn’t take long for me to realise that there was something wrong with mailto: links on any web page (and also any mailto: link within html emails.
I’m sure there is a setting (or a registry entry), to fix up the mailto: association.
I tried the following steps until it started to work:
Start -> Default Programs -> Set Program access and computer defaults -> Custom -> default email program (you need to scroll down for this) -> set registry values to default.
Control Panel -> Default Programs -> set your default programs -> select windows mail (or your normal email client) -> Choose defaults for this program -> make sure all boxes are ticked (eg .eml, mailto:, email link)
Control Panel -> internet options -> Advanced -> Reset