I tried to update my ipad 3.22 to 4.2.1.
I have my SHSH saved.

Started TSS server in tinyumbrella, shift+UPDATE and pointed to 4.2.1, but i have error 21. Then entered recovery mode, then kick it out using tinyumbrella.
My ipad is in normal stage during the update.
Is it i need to make my ipad to enter DFU for the update?