Hi,
What you have to understand the three-tier concept when working with NAV 2013 (and NAV 2009 RTC). Here you have the SQL database, the NAV server and the NAV client. All code is running on the NAV server, the client is only the presentation tier.
This means that in order for your code above to work, then the file must be on the NAV server, and that the user running the NAV server needs permissions to read/write files. It also means that the file you export from the code above, will be written to the “C:\temp…” on the NAV server, not on the client.