if you want to create a new entity with the filename "again.bmp" that's the correct code:

Code:
function button_3()
{
   ent_create("again.bmp",temp,NULL); 
}


if you want to show the VIEW-ENTITY you've defined above, that's the correct code
Code:
function button3()
{
   set(again_ent,VISIBLE); //you've already created the VIEW ent (note: that's not the way you decalare
//a normal level entity!) by declaring the struct, so you just have to make it visible :)
}