Same problem. In my case, the first link opens quickly; but subsequent links in the same Excel file produce the brief freeze and then . . . error . . . "This file cannot be found." If I wait for about 20 seconds on this otherwise very fast machine, Acrobat Reader belatedly displays the PDF.
My fix is tantamount to uninstalling Reader X.
I also use Acrobat Pro 9.0, so I opened Acrobat Reader X > Preferences > General > Select default PDF Handler > changed this to Acrobat 9 Pro; and waited several minutes while 'installed' Acrobat 9 Pro. After a restart, Reader X no longer gets in the way, and these shortcut links to PDF files open fine in Acrobat Pro. I also told Windows to always open PDFs in Acrobat Pro.
OS: Windows 7 Ultimate (64 bit)
Excel 2007 12.0.6545.5000 SP2
Installed Acrobat: C:\Program Files (x86)\Adobe\Acrobat 9.0\Acrobat\Acrobat.exe
Creation Date: 2010/10/06
Creation Time: 8:20:15 PM
Installed Acrobat: C:\Program Files (x86)\Adobe\Reader 10.0\Reader\AcroRd32.exe
Creation Date: 2010/11/10
Creation Time: 12:49:36 PM
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