Oh Dear mother of god.

[NosePicker5555]

I just went to go on my DW20 world when it updated and....

I logged in and I got two buttons.

Yes/No.

This is freaky-man..

Help.[DOUBLEPOST=1356859269][/DOUBLEPOST]I haven't clicked yet.

 

[Rikki21]

ID mismatch thing. Yes means ignore and enter the world anyway, supposedly it'll delete any blocks placed that are the IDs in conflict.

It shouldn't effect your game too badly, but backup your world anyway. Or wait until FTB resolves it.