I get this, upon client startup:

http://pastebin.com/pAsSBdZx

Do you use id resolver?

Sorry for the late reply. No, I use IDfix:

http://www.minecraftforum.net/topic/1928632-162smpforge-idfix-resolve-id-conflicts-automatically/

I'd think that if it was an ID conflict, it would tell me. But that's maybe not the case, since you're asking?

have you tried using the default minecraft launcher rather then the magic launcher

t999uk: I have not. I'll try that.

http://www.minecraftforum.net/topic/1831791-152buildcraft-logistics-pipes/page__st__260#entry24276318 that's all i curently know.

Looks like the same error:

http://pastebin.com/TD1bAvSA

Tried with the vanilla launcher. Same result. Also tried setting the block ID manually, just to see if that was causing the issue with my IDfix. I did not touch the item IDs though.

Right, found out that it bugs with IDfix. For some reason it's working now, with IDfix. Maybe it's because I manually assigned IDs for Logistics Pipes manually in IDfix. Closing this issue.