Sometimes it takes them longer to adjust to being handled, and not all snakes enjoy handling as much as others. What you're describing sounds like a snake that just hasn't adjusted to being handled yet. Patience, and try and support as much of the snake's body as you can while you're holding it. If you're supporting the snake's body and otherwise handling it in a calm manner, it should be just fine - just needs more time to get accustomed to handling.

-Jen