when you write inventor, do you mean "Autodesk Inventor" or "Open Inventor"?
I guess the file is some kind of assembly, which is exported as a single STL file. STL does not support multi-part models, so you would need to export each part a separate STL file (or other format supported by Sim4Life), or you export it to a file format that supports multiple parts (ACIS .sab/.sat, STEP .step, ... VTK .vtm (multiblock)).
STL also only supports triangle surface representations, so if you had a NURBS CAD file, you loose the that by exporting to STL.
Searching for the topic I found this information for Autodesk Inventor to export as a multibody sab file:
btw. if the points in different parts aren't coincident, you may be lucky with your single STL file: try Modeling -> Mesh Tools -> Separate Meshes. This could separate disconnected parts.