Check the "Disabled Items" in your Office application (File > Options > Add-ins > Manage: Disabled Items). Sometimes Office disables the runtime if it perceives a slow startup.
Because this architecture connects multiple decoupled systems (the OS, the .NET framework, Office, and the developer's source file), errors can pop up due to missing system updates or corrupt installation profiles. 1. Add-in Disappears / "Load Behavior: Unloaded" microsoft visual studio 2010 tools for office runtime -x64-
A 64-bit version of Office requires the 64-bit runtime to properly bridge the custom assemblies into the Office application process space. Check the "Disabled Items" in your Office application
Developer benefits
The represents a pivotal piece of software history, marking the transition of Office extensibility into the 64-bit era. While it has been succeeded by newer runtimes and is approaching the end of its extended support lifecycle, it remains a critical dependency for a vast catalog of enterprise software. Understanding its architecture, deployment constraints, and interplay with the .NET Framework is essential for maintaining legacy applications and planning migration strategies toward modern web-based add-in models (Office JS). While it has been succeeded by newer runtimes