I suggest you DO NOT install the previewer the first time, to check if that is what causes the error message.
Check all is working well by saving pdf attachments from e-mail and view them as if a standard user.
No error message should appear at that point since both should be standalone applications.
Now if you were using the previewer ( like an Outlook user), uninstall again and reinstall a second time with the preview option activated.
Again no error message should appear at that point.