When attempting to insert a bolt connection, fastener, gear or other part from Design Accelerator resp. Content Center, the error window is displayed:
Design Accelerator Doctor
Modeling: Failed to insert a part into assembly!
This may be caused by a damaged Design Accelerator component, by misconfigured project libraries, by wrong path to Content Center files, or by a damaged assembly. But if such error occurs in Inventor 2018 or 2019 after a Windows update, the most likely cause is the Windows update to the build 1903 (resp. higher).
In this case please update your Inventor 2018 to the version 2018.3.6 (or higher) and Inventor 2019 to the version 2019.4 (or higher).