Why am I getting these errors?

[Hotelmariofan]

First I was just wondering why the delete mode (trash can at the top left) doesn't work. If I drag an item over it and let go when it says delete item, the item goes away, until I hit E, then it just drops. If I click on the trash can to turn on delete mode, if I shift click to delete an item, it goes away. Or so I thought, because it's actually only making it invisible in my inventory. I can't pick up anything, but when I try to put something in that slot, it becomes visible again. Any idea why this is happening and how to fix it?

Also, I get messages upon my server starting up saying things like this

"RedPowerCore: MinecraftForge minor version mismatch, expecting 3.1.x, may lead to unexpected behavior" and

"20:04:53 [iNFO] CONFLICT @ -78 item slot already occupied by net.minecraft.server.ItemBlock@6b35456b while adding codechicken.enderstorage.ItemEnderChest@7660aa

c9"

while my server starts up and I can play normally, will those errors effect any items whenever I eventually start using(or trying to use) them? Thanks in advanced.

[Hushful]

When you go into "delete" mode, you just have to left click the item in your inventory.