This can happen when Adobe Reader is not fully installed on your computer or if your Adobe Reader installation is corrupted.
Solution:
If the above did not fix your problem, make sure that your Internet Security settings are allowing ActiveX controls to be ran on your computer.
Solution:
It is possible that a PDF viewer other than Adobe Reader has been installed on your computer.
The following registry patch sets Adobe Reader as the default PDF viewer for Secure-eBook and Web Pages.