I downloaded the mod and I'm certain i installed it correctly being i can craft the backpack. my problem is though i can't equip the backpack, nor can i access the inventory by right clicking with it in hand.

Have same problem

This is VERY strange. Can I see a list of other mods you guys have?
Or is there something else you are using? Are you in server/singleplayer? Need more info.

I think I figured it out though I'm not sure if this is your problem Brayferd. i really like this mod a lot and wanted it to work so i re downloaded it and switched over to the new file, and then tried it worked. come to find out though if your looking at a block even if its right outside your range it will try to place to backpack. Try looking at something really far or in the sky. How ever i had some problems with taking the backpack from the "TooManyItems" NEI and i could not craft with them. but for reference i was using:
Too many items. - Marglyph
CraftGuide. - Uristqwerty
Minions mod. - AtomicStryker
Balkon’s WeaponMod. - BalkondeurAlpha

I did uninstall TMI and everything is working wonderfully. its an awesome mod.

Got it, was trying to drag&drop it to wear. I look in the distance and R-clicked and seen the equip button, works just fine! thanks

Yea and not gonna lie having it in its own slot so you can wear a full armour set with it is awesome. And I also noticed that it places itself when you die if your not under water.