My guess is that he is about to shed. When mine shed they stay more near the ground and can't climb well. This is probably the case, but he may just be clumsy! A few of mine don't always make it to where they want!
:My new crestie is having problems climbing. At night whaen I go to give him crix or try to handle him he runs and tries to climb the glass but when he tries it is like he can't get grip. He had the same problem on my arm the other day too. He finally gets on the glass but it take a while. And he is having problems jumping when I hold him. He tries to jump from one arm to another but every once in a while he misses. Is this stuff normal???????