Sometimes the most frustrating issues are those without any error messages.
Working with a client to add a new desktop model to the SCCM build process, we found that we could not add drivers to the boot image. No error messages, greyed out buttons.
We verified security settings, restarted the Configuration Manager Console and even restarted the server without success. Luckily, the solution was one tab away.
Clicking Reload on the Images tab resolved the issue. It turns out the WIM file was updated through DISM.exe, so SCCM needed to reload for any changes, before any other changes could be made through the Configuration Manager Console.