I run a college cabling course, and I do have the students crimp 8P8C mod ends on both solid and stranded cable with the appropriate type of mod ends. I'm pretty sure I've seen every which way that someone can mess up a crimp. When the students have opens on the solid wire, I can crimp again with a bit more force and that typically solves the problem. My students use the Ideal CrimpMaster tools, and you need to apply quite a bit of force. What I actually tell them is to squeeze the the crimpers until they hear a popping sound...from their hand not the tool. It's a slight exaggeration, but you get the point.
Sometimes with solid wire you can do absolutely everything right, and you still get an open. If you have cheap plugs, this is even more likely. What basically happens is the blades on the plug go a little bit wide, and instead of contacting the copper they leave a little skin of insulation between the blade and the conductor. Sometimes this shows up as an intermittent problem, or high attenuation on one pair. You really have no control over this, although buying better quality plugs will help.
My advice is to avoid crimping mod plugs on solid cable unless absolutely necessary. Making custom cables for phone system installation is acceptable. Solid conductor patch cables, even with the best mod plugs, is never acceptable. In my experience, problems with mod plugs on solid Cat3 are much less likely than with Cat5e.
