If you work with Inventor for long enough, you’ll come across this pesky message, denying you access to the Bill of Materials (BOM) inside your assembly file. So you obediently save the assembly and try again. Same message. You run a rebuild of the file? Same message. You close and open the assembly again? Same message!
Well, frustrating as it is – there seems to be a reliable exit from this loop of doom: Switch to the ‘Master’ level of detail LOD and try again. Then switch back to your initial level of detail after you’re finished in the BOM. Does that work for you too?