Thanks, this thread from 7 years ago helped me out today.   I have a package that has some project parameters.  It ran great from visual studio... it even ran great when I deployed it to our server and set it up in a SQL job.   The job/package failed when I went in to the job and overrode the project parameters (I needed to put in new values to run the package in our QA environment).   What finally worked was using a double \\ at the end of the project parameter where I was setting the file source, and destination paths.