this problem happened with map designer in beta 3.0/1.14.in 1.15/entrenchment 1.0 & 1.01 the cause of the lockup has been fixed
the solution for beta 3 was to remove the galaxy files from the following directories,
C:\Documents and Settings\"user name"\Local Settings\Application Data\Ironclad Games\Sins of a Solar Empire\Galaxy (xp) or
C:\users\"user name"\Local Settings\Application Data\Ironclad Games\Sins of a Solar Empire\Galaxy(vista/windows7).
hope this helps
harpo