I dont know
But it says gtkradiant is not a real 32bit program
Otherwise it says something like:
missed <something>.dll
However radiant 1.3.8 works fine on my old computer
But it cant write to program files at the new 
Not even save,
Gtkradiant is like windows vista, it doesnt work,
and if it works it dont work fully
I dont know why radiant use dlls
they are old, microsoft wants to remove them
All mappers isnt people that got 700% time to look after missed dlls
I think radiants team have to rethink their concept
Radiant should be easy to install, just like photoshop or minecraft…