Import flat file from (fixed length) from my PC

I'm using the Flat File Importer in the app store to import a file (it populates one entity).  it works perfectly fine when i'm running it locally.  On "Test Execution" the importer pulls a file from my C Drive and imports.  When i go run it in my sandbox (free app) the "import directory cannot be found".  Is there a setting that i'm missing?  Can i even do this in a free app?