No Disk in Drive Error

Acrobat XI with 11.0.01 patch applied

Windows 7 x64

Deployed to about 1100 machines via MS SCCM.

When opening PDFs a lot of users are receiving error messages about not having a disk in drives A:\ and D:\ even though they opened the PDF from their C:\ drive. After clicking OK the PDF does eventually open.

We noticed that if we turn off Protected Mode these errors go away but for a number of reasons we will not be turning off protected mode.

Please advise.

Thanks.