They have a problem just before shedding (simple sign of shed coming) and if you have any film left on the glass from cleaning the cage. Make sure you wipe it clean.
Also, improper humidity (to low), a dusty enviornment (unrinsed bark and such) will effect thier ability to stick since static is what makes thier feet work. Quick test of this is to mist the cage well and then see if he can walk on the glass.
:My crested rocky seems only to be able ot climb on the glass in his home after he sheds is this normal, if not what can i do to help him cuz he seems to get pissed whe he jump and slides instead of jump adn sticks thanks latter