Tekkit 2.0 to 2.1.1 update problem

[PewnyPL]

Hello everyone.

For quite some time I have been using Tekkit 2.0 as a server and finally decided to update it to 2.1.1 but... my world didn't like it. Literally every non-vanilla block from the world is gone! IC2 machines are just black blocks you can go through, blocks like marble or ores are literally missing, like if replaced with air. I can, using NEI, spawn IC2 or RedPower items, also when going towards a new, not yet generated chunk, the ores from mods and such do appear.

So my question is, did the IDs of blocks changed between versions? If so, is there a way to fix it or do I have to make a new world? (Note: None of block IDs were changed by me when making the 2.0 server, aside from the Computer Craft fix, which literally changed IDs of 2 blocks)

[PewnyPL]

Nevermind, found the problem.

Someone else logged into the server, and found that their INVENTORY still had it's IC2 and RedPower items. I guess that during the first launch for some reason mods didn't load and all non-vanilla blocks werereplaced with air... And then server upon exit overwrote all chunks.