There could be a number of reasons for the doors not operating correctly.
Assuming that they do at least try. ie NOT an electronic fault then the primary rubber drive bands could have stretched/gone hard/broken. These can be replaced with spares from your dealer. Order spares for a 9300, they are the same!
The drive strings may have broken/dropped off of the wheels. These can also be replaced with spares items for the 9300. Warning - considerable patience and manual dexterity is required to replace these so DO NOT proceed with gay abandon.
The slide channels may be clogged with dust/grime. Clean out with cotton wool bud damped with isopropanol. Lubricate with nothing more than silicone spray applied with a cotton bud (ie spray onto the bud and applied to the channels)
Hope this helps