I can’t open email attached file using opera

Hello everyone,
I use Opera 9.6 for browsing the Internet. Most of the time, I receive email with attachments. When I received those attachment, I want to open it instantly from the open file feature of the browser. A while ago when I am about to open the file, I meet an error that said, No registered application for this extension.

No registered application for this extension.
I am now wondering, why I can't open the file, I tried using other browser, it opened.
I removed the opera and installed it again, same error message when I open email attached file. I also checked on some restriction on my firewall, there was no restriction in opening email attached file.
Please help me solve my issue.
Thanks.
