OS: Windows 8.1 x64 pro
MC Version: 1.7.10
Forge: 10.13.0.1199.
Game mode: Creative
On Server/Client: Server
Railcraft version: 9.2.1.0
Forestry version: 2.4.2.31

Game crashes your client when you click the 'creative search' button, due to (as far as I can tell) a mod-interaction bug between Railcraft and Forestry involving Forestry backpacks. Server remains up. Worked fine without crashing before updating Railcraft from 9.2.0.0 to 9.2.1.0.

Full FML log was too large to post (It was >500kb), but here is the crash report: http://pastebin.com/z7znjffx.
Openeye report: http://openeye.openmods.info/crashes/97fc6af169ce54d8e6dffaa2437d60cc

I have the same bug. Tried also forestry 2.4.2.44 - same.
Helps only downgrade version railcraft.

Disabling the Railcraft Backpacks will let you play. I'll post a fix tomorrow.

I think this has this been reolved now.

Yep.