In your Internet Browser settings (I use IE). Under Options/Programs/Manage Add Ons. I in the list of progrms you shodul see Adobe PDF Reader as type ActiveX control. Make sure that this is enabled. If it is not there then it was never installed. Your system may be blocking the install of the ActiveX controls if it is not there.
just to avoid starting a new thread, I am posting a associated question, even I am preety new to LS world. I earlier had acrobat 7.0, after installing LS desginer. I uninstalled 7.0 and installed acrobat 8.1, but on preview tab when I right click and view "document properties" version shows 7.x. I wonder if LS designer actually previews with my 8.1 acrobat or not?. Is this correct?.