I'm sorry to bring this up again, but the same crash I posted about has happened again. Same Ruin type as before.(This is the taiga map that is there when installing the pack). This is a newly gen chunk without Fastcraft installed(Removed it after the first crash). Sorry I can't give you anymore info. Its the drying rack or what ever is trying to spawn on the rack itself. I spent a couple hours trying to get any info on what it might be to help you out, but failed.
Just to be clear, this ruin is the tall Harden Clay/Bedrock/Red Sand, with a small slab damaged staircase going up, and down. The Rack is under this ruin in the same place as the last one I removed with McEdit. Sorry again.. I tried figuring out how/what all can spawn on the drying racks as well, but couldn't figure out (if there is) a list or not. I will keep looking into it in hopes that I can help better.
It took me awhile, but just to some what help, I did re-install the pack and then fly around to try and find that tower and I finally found one and it was a crash to desktop as before. Will keep looking into it.
Update: If I'm doing this right this is what I have found out. Item ID 4478 DMG 4 Unknown Item 4478:4. This is what is trying to load on the Tinkers Rack. When searching the Item ID's that is a Blank Pattern. That is all I can figure out.
You've provided plenty of information. There is indeed a possibility that a blank pattern can be on a rack in the Spire. I've played this game plenty of times and found Blank patterns and to date they haven't crashed the game.
As mentioned before, most of the crashes I've personally experienced have been as a result of ruins spawning over Buildcraft's sludge or sewage pools. In an attempt to minimise such conflicts, I've removed naturally spawning sludge and sewage and replaced them with custom ruins in the 1.4.0 update. This won't help you now but the only other thing I would suggest is trying a different biome. Its doubtful the blank pattern would be the single cause of your crash as its hasn't been reported by anyone else so far. It might simply have been the last thing trying to load before the crash.
Usually when the game crashes due to a ruins conflict, the game can still be played and will re-open again. Sometimes the crash is caused by a the game running out of memory which would be unique to a computer. You may have noticed as you approached a ruin that your game slowed before crashing. This is typical of a memory overload.
There are so many possibilities as to why a crash occurs. I've had this happen with other FTB games as well. I've set my computer to use just 4 GB of memory and limited its speed to 60FPS and it still manages to crash from time to time.
Hopefully the update will be more stable on your computer.
Keep looking into it though, I'm interested in finding out if there's a cause that can be rectified by changing something in the ruin or updating to a more stable version.
I'd also like to know if anyone has any idea what causes those long black voids to appear randomly in a game.