Help resolving files in inventor 2017

Last spring I downloaded an assembly of a wheel from the andymark website as a step file and then saved it in inventor 2016 as an .iam file. When I try to open it in inventor 2017, it says that the assembly is unresolved and will not display the parts.
I tried to simply download the part again, but when I saved it as an .iam it still read it as unresolved. This makes me think that either the file is faulty or there is something I don’t know about with how the update affects saved files.
Does anybody know what I could do about this?

when it says “unresolved” it usually means that the parts are not where it is looking for them, and thus cannot display them.

Are you using a project file? This has an ipj extension and manages where files are located.

I don’t think I’m using a project file (I don’t currently have access to it to check definitively), but I do recall seeing something about a project in the “unresolved” message.

Should I be using a project file?