What might seam;
The adapters are larger than the original plug of the docking cable.
If the iPad used in a silicone shell etc., the cut is not big enough for the direct connection of the adapter for the dock connector.
The available Internet Dock Extender (extension cable male-female) are usually not 30-pin wired (sh. Recessions), so that only charging and sync is possible. But a few more contacts are required for transmitting the images.
So either buy a dock extender, the wired and fully plug is small enough or the iPad always take out of the sheath.