Can't Login.

There are a few things that could cause this. If your farm is large enough, it may be lagging your machine and it may have run out of memory. Alternatively, the problem could be a corrupted chunk, block or mob.
A easier way to find out is to post your crash report.
@Tyler

 

Ya some texture packs do that.

 

It's common with most texture packs lately

 

I know some textures disconnect you.

 

i know which one?

 

Simple textures such as pixel-based textures or plain 16-bit textures should run fine on the average computer. 32-bit and higher tend to cause problems, which the explanation for should be obvious.

Basically, don't use too detailed of textures if your machine is already having a hard time running the game itself.