I have Acrobat Reader XI on a Windows XP system. Could open PDFs fine until this week. I get a message that says I need to open it with protected mode disabled. If I do that I get an error message that says: Acrobat failed to load its CORE DLL. I tried to get Acrobat Reader XI to repair itself in the add/remove programs section, but get a message that says 'this patch pkg could not be opened'. So, the next solution listed on the acrobat website was to check for rootkits, so I did a scan with Kaspersky. It came up clean. The next solution says to remove and reinstall. I'm a little leery about doing that since am not sure the most current Acrobat software will load on XP. Yes, I know I am using an outdated operating system, but love Outlook Express. I use it to run a continuing education program. And OE only runs on XP. Any ideas you have will be appreciated. THANK YOU!