If you have not tried the above steps yet, then I have an alternative. Try reverting back to an old save point prior to the date you lost your scanning abilities.
I have seen a runtime error on Windows 8 where the OS was refreshed and that fixed the issue. In Windows 7, refresh is like reverting back to an old save point. You can also choose to upgrade your Windows 7 OS to Windows 7 OS (that is not an error in typing). This restores the important original settings prior to the possibility that perhaps a Windows update to C++ is what caused this.
You also have the option of using a recovery CD as well. The link(s) below may also be helpful.
Let me know if these are also options. Since you have a lot of HP printers, yes my steps above would cause you to have to re-install the software to every last one of them. I want to make this as easy as possible for you but if the above suggestions do not work, it may have to be done. Keep me posted though. I hope this works!