So, with all the playing of Industrialcraft/Buildcraft I've been doing lately, I decided it would be soooo much cooler to move my world onto the server so that all the mining and stuff would keep going while I wasn't there. It would be so nice to just setup a miner, and come back later to a chest full of goodies. The big problem is, I just finally got my first quarry setup in the SSP world I setup, so I didn't want to lose all that progress. I went through all the steps, setup the server and WHAM! crash. Buildcraft wasn't happy. I was running my SSP in 2.2.0 and the server in 2.2.1, not sure if that's the problem, but trying to move my SSP over to the server as the world there just didn't work. Java errors every time I started it up. As a test, I decided to just start a new world with the same seed. World loaded up fine, no crashes, so I jumped in it, and the world was totally different. I have a feeling that the world gen code portion of one of the mods is different enough to completely change the world. Now, in a new world, none of the crafted stuff for buildcraft is there, so it's possible that as soon as I try to get a setup going like I had in my old world, it'll just totally crash again.
As an added measure of testing, I updated my SSP game to 2.2.1 and loaded up the world and it came up just fine, so I'm at a loss as to what I should do. I did see that according to SpaceToad, 2.2.1 is still really buggy, so maybe an update or two will get it so much world will work, but I think I'd rather start over in a fresh world on the server than keep playing my existing world, and lose it to move to the server at a later date.
ETA: Wow, not sure what happened, but in the end after all the playing with everything I connected back to the server and it's the same world! Empty, yeah, but the same, which is really cool, cause I LOVE the starting place for that seed.