Why do you open a new topic ?!?!

Change
if (mouse_map == shield_pcx)
{
on_mouse_middle= delete_shield; // wegwerfen des schildes bei rechter maustaste ///////////////
}

to:

if (mouse_map == shield_pcx)
{
if(mouse_middle) {
delete_shield();
while(mouse_middle) { wait(1); }
}
}