MiKTeX comes with the 2 files pdfopen and psdfclose.exe in its "bin" folder. These programs worked fine until now, but after an upgrade to Adobe Reader XI they fail.
I cannot find the source files of these programs to update them but I found that this has already been done because in
support Adobe Reader XI and Adobe Acrobat XI in pdfopen and pdfclose."
So perhaps it is enough to grab the fixed files there and ship them with the next MikTeX update.