Please attach the required part files as well. Keep in mind that an assembly file is just an empty "bucket" into which you place other files and then assemble them.
It's also generally a good idea to state the version of Inventor you are using so that someone with Inventor 2013 does not work up a soloution for you that you could not access if you had Inventor 2012, for instance.
I hope this helps.
Best of luck to you in all of your Inventor pursuits,
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