Not sure if this is a BC or WAILA issue - crossposted to both issue trackers.

SMP client is crashing when looking at BuildCraft 6.1.4 items. Other items seem to be unaffected. Strangely, I have not been able to reproduce this bug using Windows - only Mac. I've duplicated this bug using both my personal Mac Air, and my fiancee's iMac. Issue did not occur until we installed the new version of BuildCraft to the server. For what it's worth, that version is still in beta.

I'm not sure that the actual BC item matters, but this is occurring for -any- BC item - I duplicated this problem by looking at the cobblestone pipe.

I wasn't sure which of these you needed, so here are pastebins from the Game Output tab, the Crash Report tab, and the actual Crash Report text file generated.

http://pastebin.com/Gp9deeMY
http://pastebin.com/KgmWHGVq
http://pastebin.com/8Nfgip4L

This is the same issue as #2105, it's because you're using an old Java version. The crash has been fixed however, and will no longer happen as of BuildCraft 6.1.5 (not yet released)

Thanks for the reply. I'm confused though - I've installed the newest Java RE from their site, and I'm still crashing. Are you saying I'll just have to wait util BC 6.1.5?

Yes, 6.1.5 will work with your Java.
The crash report states you have Java 6 which reached "End of Public Updates" in Feb 2013
I recommend updating to Java 7 or Java 8

Weird - I've installed (and had other players on my server install) Java 8. I'll look into gutting all of the older installations I guess. Just tried to install Java 7 Update 71 and it told me I already had 8 installed.

Edit - thanks for pointing this out in the logs. For some reason Minecraft is still using an older version of Java, despite gutting it from my system. Oracle's instructions for removal seem .. insufficient.

Indeed, they are insufficient. :)