Hi Jonathan Sparks,
I will suggest you to recreate the application preferences and clear the temp folder.
Clear the temp folder %temp%
Try repair Acrobat from MSI file. (C:\Program File (x86)\Adobe\Acrobat X\Setup Files\{some alphanumeric}\)
Run AcroPro.msi and choose repair
Restart machine and now try to combine.
Thanks,
Abhishek