Stata 13 introduced a new file format which older versions of Stata can’t open. Fortunately, there’s an easy fix: the
use13 command. In the command window, first type
ssc install use13 to install it. Then you can type
use13 SWIIDv5_0.dta, clear to load the SWIID data.
Update: Version 5.1 is saved in the older file format, so this shouldn’t be a problem anymore.