Loading and Saving my own Meshes

You can't depend on function parameters being evaluated in any particular order...

DoSomething f(x), g(x)

might call g before or f. Or maybe not.

This means you need to replace

temp_vertex=AddVertex(temp_surface,ReadFloat(file),ReadFloat(file),ReadFloat(file))

with

x# = ReadFloat(file)
y# = ReadFloat(file)
z# = ReadFloat(file)

temp_vertex = AddVertex temp_surface, x,y,z