Railcraft will crash using the Creative Search tab (not the Railcraft tab) with certain blocks disabled. From the testing I did, these blocks were the ones at fault:

B:ore_dark_diamond=false
B:ore_dark_emerald=false
B:ore_dark_lapis=false
B:ore_saltpeter=false
B:ore_sulfur=false

Other ores can still be disabled safely.

May be related to #1162.

edit: Ah, almost forgot a crash log: https://pastebin.com/su0dktz2

Merged into #1162. Thanks for the report!