I think you'll need to re-upload your file, it only contained the .SLDASM assembly file. We would need the individual part files too. Easy way to do this is to do a File -> Pack and Go operation from the assembly which will package everything up in a zip file.
From looking at your screenshot though, I can offer some general advice
Do you need to treat those two components of the arm as beams? SOLIDWORKS does that automatically if they are weldment structural members, but you can override it by right clicking the component from the Simulation tree and choosing "Treat as Solid". That's what I would recommend here as they are relatively short and stubby, and feature intricate connections that would be difficult to capture with the beam mesh.
Once they are treated as solid, the next question is - what do the contact interface between the arm and the other components look like?
If they are clean, coincident contact surfaces with no interference, they should be automatically bonded by the Global Component contact.
If the above is not true (as looks to be the case of the two tabs with the thru hole, like they may not be touching the arm or coped to it nicely) then you'll need to define local bonding.
This is done by right clicking the connections folder and choosing contact set, and selecting the face of the tab, then the face of the arm to establish a local bonded contact. You would then want to repeat this process per tab (or whatever other item) until all contacts are defined.
Properly defined contacts are one of the most important things for assembly analysis and unfortunately not very well documented in the tutorials. Though it is a big focus of the official SOLIDWORKS Simulation training class if you ever get the opportunity to take that.
You can also use the "Contact Visualization Plot" to visualize where you have contacts, and if you are missing any.
Thank you, Ryan I have re-uploaded the zip file and should contain all necessary files.
As you suggested I have attempted to treat the beams as a solid. With this configuration, I was able to run the simulation but I am seeing some rather unrealistic stress concentrations. I would assume these would disappear by modeling the weld that should be there. Is there an easy way to do this?