Maybe you are using the incorrect size crimp bead? You could look at the size string you are using and then look up what size crimp bead you should be using. Also, are you using a crimp tool or just bending the crimp bead?
Ditto what Stacy said above.Also are you maybe stringing to many wires through one crimp? Also do you use crimp beads (round) or crimp tubes? Tubes are better IMHO, especially if you crimp them properly.
Here is a tutorial on crimping properly with a crimping tool at about.com:
The switch knot is a decorative lacy macrame/ hemp jewelry knot that helps you save on twine too. This tutorial shows you how to tie one with clear pictures and instructions.
A sliding knot is a wonderfully easy way to end off a leather, string, hemp, or corded necklace or bracelet. It looks neat and stylish, is a very practical closure, and is very easy to make.