unable to fillet

 From:  crydee
2632.1 
Hello,

At first, congrulation to this piece of software. i love it.
but sometimes i have some problems with fillet. is there some trick or whatever? especially the front of the car is interessant. you can see that i could use fillet for 3 gaps but the 4th isn't working. same problem is the wheel house.

has anybody an idea what i'm doing wrong?
thanks in advance.

cheers
crydee